diff --git a/code/FormSchemaController.php b/code/FormSchemaController.php
new file mode 100644
index 000000000..4458a28ba
--- /dev/null
+++ b/code/FormSchemaController.php
@@ -0,0 +1,156 @@
+<?php
+
+namespace SilverStripe\Admin;
+
+use SilverStripe\Control\HTTPRequest;
+use SilverStripe\Control\HTTPResponse;
+use SilverStripe\Core\Validation\ValidationResult;
+use SilverStripe\Forms\Form;
+use SilverStripe\Forms\HTMLEditor\HTMLEditorConfig;
+use SilverStripe\Forms\HTMLEditor\TinyMCEConfig;
+use SilverStripe\Forms\Schema\FormSchema;
+use SilverStripe\Security\Security;
+
+/**
+ * The base class for controllers in the CMS that need access to form schema functionality.
+ */
+abstract class FormSchemaController extends AdminController
+{
+    /**
+     * Form schema header identifier
+     */
+    public const SCHEMA_HEADER = 'X-Formschema-Request';
+
+    private static array $allowed_actions = [
+        'schema',
+    ];
+
+    private static array $url_handlers = [
+        'GET schema/$FormName/$ItemID/$OtherItemID' => 'schema',
+    ];
+
+    private static array $dependencies = [
+        'FormSchema' => '%$' . FormSchema::class,
+    ];
+
+    /**
+     * Current form schema helper
+     */
+    private ?FormSchema $schema = null;
+
+    protected function init()
+    {
+        $this->beforeExtending('onInit', function () {
+            $this->prepareTinyMce();
+        });
+        parent::init();
+    }
+
+    /**
+     * Get the form schema helper for this controller
+     */
+    public function getFormSchema(): FormSchema
+    {
+        if (!$this->schema) {
+            $this->schema = FormSchema::singleton();
+        }
+        return $this->schema;
+    }
+
+    /**
+     * Set the form schema helper for this controller
+     */
+    public function setFormSchema(FormSchema $schema): static
+    {
+        $this->schema = $schema;
+        return $this;
+    }
+
+    /**
+     * Gets a JSON schema representing the current edit form.
+     */
+    public function schema(HTTPRequest $request): HTTPResponse
+    {
+        $formName = $request->param('FormName');
+        $itemID = $request->param('ItemID');
+
+        if (!$formName) {
+            $this->jsonError(400, 'Missing request params');
+        }
+
+        // Most usages of this method (e.g. AssetAdmin) have two methods - one method is
+        // named the same as the form, and does not accept a parameter - the other prefixed
+        // with "get" and accepts an $itemID parameter.
+        // Some usages exclude the getter method, so we need to check for both.
+        $formMethod = "get{$formName}";
+        if (!$this->hasMethod($formMethod)) {
+            $formMethod = $formName;
+            if (!$this->hasMethod($formMethod)) {
+                $this->jsonError(404, 'Form not found');
+            }
+        }
+
+        if (!$this->hasAction($formName)) {
+            $this->jsonError(401, 'Form not accessible');
+        }
+
+        if ($itemID) {
+            $form = $this->{$formMethod}($itemID);
+        } else {
+            $form = $this->{$formMethod}();
+        }
+        $schemaID = $request->getURL();
+        return $this->getSchemaResponse($schemaID, $form);
+    }
+
+    /**
+     * Check if the current request has a X-Formschema-Request header set.
+     * Used by conditional logic that responds to validation results
+     */
+    protected function getSchemaRequested(): bool
+    {
+        $parts = $this->getRequest()->getHeader(static::SCHEMA_HEADER);
+        return !empty($parts);
+    }
+
+    /**
+     * Generate schema for the given form based on the X-Formschema-Request header value
+     *
+     * @param string $schemaID ID for this schema. Required.
+     * @param Form|null $form Required for 'state' or 'schema' response
+     * @param ValidationResult $errors Required for 'error' response
+     * @param array $extraData Any extra data to be merged with the schema response
+     */
+    protected function getSchemaResponse(string $schemaID, ?Form $form = null, ValidationResult $errors = null, array $extraData = []): HTTPResponse
+    {
+        $parts = $this->getRequest()->getHeader(static::SCHEMA_HEADER);
+        $data = $this
+            ->getFormSchema()
+            ->getMultipartSchema($parts, $schemaID, $form, $errors);
+
+        if ($extraData) {
+            $data = array_merge($data, $extraData);
+        }
+
+        $response = new HTTPResponse(json_encode($data));
+        $response->addHeader('Content-Type', 'application/json');
+        return $response;
+    }
+
+    private function prepareTinyMce(): void
+    {
+        // Set the members html editor config
+        if (Security::getCurrentUser()) {
+            HTMLEditorConfig::set_active_identifier(Security::getCurrentUser()->getHtmlEditorConfigForCMS());
+        }
+
+        // Set default values in the config if missing.  These things can't be defined in the config
+        // file because insufficient information exists when that is being processed
+        $htmlEditorConfig = HTMLEditorConfig::get_active();
+        $htmlEditorConfig->setOption('language', TinyMCEConfig::get_tinymce_lang());
+        $langUrl = TinyMCEConfig::get_tinymce_lang_url();
+        if ($langUrl) {
+            $htmlEditorConfig->setOption('language_url', $langUrl);
+        }
+    }
+}
diff --git a/code/LeftAndMain.php b/code/LeftAndMain.php
index e6193ee8c..0b21d5183 100644
--- a/code/LeftAndMain.php
+++ b/code/LeftAndMain.php
@@ -19,18 +19,14 @@
 use SilverStripe\Core\Injector\Injector;
 use SilverStripe\Core\Manifest\ModuleResourceLoader;
 use SilverStripe\Core\Manifest\VersionProvider;
-use SilverStripe\Dev\Deprecation;
 use SilverStripe\Dev\TestOnly;
 use SilverStripe\Forms\DropdownField;
 use SilverStripe\Forms\FieldList;
 use SilverStripe\Forms\Form;
 use SilverStripe\Forms\FormAction;
 use SilverStripe\Forms\HiddenField;
-use SilverStripe\Forms\HTMLEditor\HTMLEditorConfig;
-use SilverStripe\Forms\HTMLEditor\TinyMCEConfig;
 use SilverStripe\Forms\LiteralField;
 use SilverStripe\Forms\PrintableTransformation;
-use SilverStripe\Forms\Schema\FormSchema;
 use SilverStripe\i18n\i18n;
 use SilverStripe\Model\List\ArrayList;
 use SilverStripe\ORM\CMSPreviewable;
@@ -57,14 +53,8 @@
  * This is essentially an abstract class which should be subclassed.
  * See {@link CMSMain} for a good example.
  */
-class LeftAndMain extends AdminController implements PermissionProvider
+class LeftAndMain extends FormSchemaController implements PermissionProvider
 {
-
-    /**
-     * Form schema header identifier
-     */
-    const SCHEMA_HEADER = 'X-Formschema-Request';
-
     /**
      * Enable front-end debugging (increases verbosity) in dev mode.
      * Will be ignored in live environments.
@@ -104,7 +94,6 @@ class LeftAndMain extends AdminController implements PermissionProvider
      *
      * @config
      * @var string
-     * @deprecated 2.4.0 Will be renamed to model_class
      */
     private static $model_class = null;
 
@@ -116,32 +105,16 @@ class LeftAndMain extends AdminController implements PermissionProvider
         'save',
         'printable',
         'show',
-        'Modals',
         'EditForm',
         'AddForm',
         'batchactions',
         'BatchActionsForm',
-        'schema',
-        'methodSchema',
-    ];
-
-    private static $url_handlers = [
-        'GET schema/$FormName/$ItemID/$OtherItemID' => 'schema',
-        'GET methodSchema/$Method/$FormName/$ItemID' => 'methodSchema',
     ];
 
     private static $dependencies = [
-        'FormSchema' => '%$' . FormSchema::class,
         'VersionProvider' => '%$' . VersionProvider::class,
     ];
 
-    /**
-     * Current form schema helper
-     *
-     * @var FormSchema
-     */
-    protected $schema = null;
-
     /**
      * Current pageID for this request
      *
@@ -336,142 +309,19 @@ public function getClientConfig(): array
     {
         // Add WYSIWYG link form schema before extensions are applied
         $this->beforeExtending('updateClientConfig', function (array &$clientConfig): void {
+            $modalController = ModalController::singleton();
             $clientConfig['form'] = [
                 'EditorExternalLink' => [
-                    'schemaUrl' => $this->Link('methodSchema/Modals/EditorExternalLink'),
+                    'schemaUrl' => $modalController->Link('schema/EditorExternalLink'),
                 ],
                 'EditorEmailLink' => [
-                    'schemaUrl' => $this->Link('methodSchema/Modals/EditorEmailLink'),
+                    'schemaUrl' => $modalController->Link('schema/EditorEmailLink'),
                 ],
             ];
         });
         return parent::getClientConfig();
     }
 
-    /**
-     * Get form schema helper
-     *
-     * @return FormSchema
-     */
-    public function getFormSchema()
-    {
-        return $this->schema;
-    }
-
-    /**
-     * Set form schema helper for this controller
-     *
-     * @param FormSchema $schema
-     * @return $this
-     */
-    public function setFormSchema(FormSchema $schema)
-    {
-        $this->schema = $schema;
-        return $this;
-    }
-
-    /**
-     * Gets a JSON schema representing the current edit form.
-     */
-    public function schema(HTTPRequest $request): HTTPResponse
-    {
-        $formName = $request->param('FormName');
-        $itemID = $request->param('ItemID');
-
-        if (!$formName) {
-            $this->jsonError(400, 'Missing request params');
-        }
-
-        $formMethod = "get{$formName}";
-        if (!$this->hasMethod($formMethod)) {
-            $this->jsonError(404, 'Form not found');
-        }
-
-        if (!$this->hasAction($formName)) {
-            $this->jsonError(401, 'Form not accessible');
-        }
-
-        if ($itemID) {
-            $form = $this->{$formMethod}($itemID);
-        } else {
-            $form = $this->{$formMethod}();
-        }
-        $schemaID = $request->getURL();
-        return $this->getSchemaResponse($schemaID, $form);
-    }
-
-    /**
-     * Get the form schema from a given method.
-     * The method must return a Form.
-     */
-    public function methodSchema(HTTPRequest $request): HTTPResponse
-    {
-        Deprecation::noticeWithNoReplacment('2.4.0', 'Will be replaced with SilverStripe\Admin\FormSchemaController::schema()');
-        $method = $request->param('Method');
-        $formName = $request->param('FormName');
-        $itemID = $request->param('ItemID');
-
-        if (!$formName || !$method) {
-            $this->jsonError(400, 'Missing request params');
-        }
-
-        if (!$this->hasMethod($method)) {
-            $this->jsonError(404, 'Method not found');
-        }
-        if (!$this->hasAction($method)) {
-            $this->jsonError(401, 'Method not accessible');
-        }
-
-        $methodItem = $this->{$method}();
-        if (!$methodItem->hasMethod($formName)) {
-            $this->jsonError(404, 'Form not found');
-        }
-        if (!$methodItem->hasAction($formName)) {
-            $this->jsonError(401, 'Form not accessible');
-        }
-
-        $form = $methodItem->{$formName}($itemID);
-        $schemaID = $request->getURL();
-
-        return $this->getSchemaResponse($schemaID, $form);
-    }
-
-    /**
-     * Check if the current request has a X-Formschema-Request header set.
-     * Used by conditional logic that responds to validation results
-     *
-     * @return bool
-     */
-    protected function getSchemaRequested()
-    {
-        $parts = $this->getRequest()->getHeader(static::SCHEMA_HEADER);
-        return !empty($parts);
-    }
-
-    /**
-     * Generate schema for the given form based on the X-Formschema-Request header value
-     *
-     * @param string $schemaID ID for this schema. Required.
-     * @param Form $form Required for 'state' or 'schema' response
-     * @param ValidationResult $errors Required for 'error' response
-     * @param array $extraData Any extra data to be merged with the schema response
-     */
-    protected function getSchemaResponse($schemaID, $form = null, ValidationResult $errors = null, $extraData = []): HTTPResponse
-    {
-        $parts = $this->getRequest()->getHeader(static::SCHEMA_HEADER);
-        $data = $this
-            ->getFormSchema()
-            ->getMultipartSchema($parts, $schemaID, $form, $errors);
-
-        if ($extraData) {
-            $data = array_merge($data, $extraData);
-        }
-
-        $response = new HTTPResponse(json_encode($data));
-        $response->addHeader('Content-Type', 'application/json');
-        return $response;
-    }
-
     /**
      * Try to redirect to an appropriate admin section if we can't access this one
      */
@@ -499,20 +349,6 @@ protected function init()
                 $this->extend('accessedCMS');
             }
 
-            // Set the members html editor config
-            if (Security::getCurrentUser()) {
-                HTMLEditorConfig::set_active_identifier(Security::getCurrentUser()->getHtmlEditorConfigForCMS());
-            }
-
-            // Set default values in the config if missing.  These things can't be defined in the config
-            // file because insufficient information exists when that is being processed
-            $htmlEditorConfig = HTMLEditorConfig::get_active();
-            $htmlEditorConfig->setOption('language', TinyMCEConfig::get_tinymce_lang());
-            $langUrl = TinyMCEConfig::get_tinymce_lang_url();
-            if ($langUrl) {
-                $htmlEditorConfig->setOption('language_url', $langUrl);
-            }
-
             Requirements::customScript("
                 window.ss = window.ss || {};
                 window.ss.config = " . $this->getCombinedClientConfig() . ";
@@ -1261,18 +1097,6 @@ public function EmptyForm()
         return $form;
     }
 
-    /**
-     * Handler for all global modals
-     *
-     * @return ModalController
-     * @deprecated 2.4.0 Will be removed without equivalent functionality to replace it
-     */
-    public function Modals()
-    {
-        Deprecation::noticeWithNoReplacment('2.4.0');
-        return ModalController::create($this, "Modals");
-    }
-
     /**
      * Renders a panel containing tools which apply to all displayed
      * "content" (mostly through {@link EditForm()}), for example a tree navigation or a filter panel.
diff --git a/code/ModalController.php b/code/ModalController.php
index 1ed88c5c3..34e85e3a3 100644
--- a/code/ModalController.php
+++ b/code/ModalController.php
@@ -4,107 +4,48 @@
 
 use SilverStripe\Admin\Forms\EditorEmailLinkFormFactory;
 use SilverStripe\Admin\Forms\EditorExternalLinkFormFactory;
-use SilverStripe\Control\Controller;
-use SilverStripe\Control\RequestHandler;
-use SilverStripe\Dev\Deprecation;
 use SilverStripe\Forms\Form;
 
 /**
  * Parent controller for all CMS-global modals
  */
-class ModalController extends RequestHandler
+class ModalController extends FormSchemaController
 {
+    private static ?string $url_segment = 'modals';
+
     private static $allowed_actions = [
         'EditorExternalLink',
         'EditorEmailLink',
     ];
 
-    public function Link($action = null)
-    {
-        return Controller::join_links(
-            $this->getController()->Link(),
-            $this->getName(),
-            $action,
-            '/'
-        );
-    }
-
-    /**
-     * @var Controller
-     * @deprecated 2.4.0 Will be removed without equivalent functionality to replace it
-     */
-    protected $controller;
-
-    /**
-     * @var string
-     */
-    protected $name;
-
-    public function __construct($controller, $name)
-    {
-        parent::__construct();
-
-        $this->controller = $controller;
-        $this->name = $name;
-    }
-
-    public function getRequest()
-    {
-        return $this->controller->getRequest();
-    }
-
-    /**
-     * @return Controller
-     * @deprecated 2.4.0 Will be removed without equivalent functionality to replace it
-     */
-    public function getController()
-    {
-        Deprecation::noticeWithNoReplacment('2.4.0');
-        return $this->controller;
-    }
-
-    /**
-     * Get urlsegment
-     *
-     * @return string
-     * @deprecated 2.4.0 Will be removed without equivalent functionality to replace it
-     */
-    public function getName()
-    {
-        Deprecation::noticeWithNoReplacment('2.4.0');
-        return $this->name;
-    }
+    private static string $required_permission_codes = 'CMS_ACCESS';
 
     /**
      * Builds and returns the external link form
-     *
-     * @return Form
      */
-    public function EditorExternalLink()
+    public function EditorExternalLink(): Form
     {
         // Show link text field if requested
-        $showLinkText = $this->controller->getRequest()->getVar('requireLinkText');
+        $showLinkText = $this->getRequest()->getVar('requireLinkText');
         $factory = EditorExternalLinkFormFactory::singleton();
         return $factory->getForm(
-            $this->controller,
-            "{$this->name}/EditorExternalLink",
+            $this,
+            __FUNCTION__,
             [ 'RequireLinkText' => isset($showLinkText) ]
         );
     }
 
     /**
      * Builds and returns the external link form
-     *
-     * @return Form
      */
-    public function EditorEmailLink()
+    public function EditorEmailLink(): Form
     {
         // Show link text field if requested
-        $showLinkText = $this->controller->getRequest()->getVar('requireLinkText');
+        $showLinkText = $this->getRequest()->getVar('requireLinkText');
         $factory = EditorEmailLinkFormFactory::singleton();
         return $factory->getForm(
-            $this->controller,
-            "{$this->name}/EditorEmailLink",
+            $this,
+            __FUNCTION__,
             [ 'RequireLinkText' => isset($showLinkText) ]
         );
     }