Global Configuration in Admin UI Classic

You can add a Global Configuration for all WYSIWYG Editors for all documents by setting pimcore.document.editables.wysiwyg.defaultEditorConfig. You can add a Global Configuration for all WYSIWYG Editors for all data objects by setting pimcore.object.tags.wysiwyg.defaultEditorConfig.

For this purpose, you can create a Pimcore Bundle and add the configuration in a file in the Resources/public directory of your bundle (e.g. Resources/public/js/editmode.js).

pimcore.document.editables.wysiwyg = pimcore.document.editables.wysiwyg || {};
pimcore.document.editables.wysiwyg.defaultEditorConfig = { menubar: true };

This will show you the default menubar from TinyMCE in all document editables.

For the data object settings, you should put them in the startup.js in your bundle.

pimcore.registerNS("pimcore.plugin.YourTinymceEditorConfigBundle");

pimcore.plugin.YourTinymceEditorConfigBundle = Class.create({

    initialize: function () {
        document.addEventListener(pimcore.events.pimcoreReady, this.pimcoreReady.bind(this));
    },

    pimcoreReady: function (e) {
        pimcore.object.tags.wysiwyg = pimcore.object.tags.wysiwyg || {};
        pimcore.object.tags.wysiwyg.defaultEditorConfig = { menubar: true };
    }
});

const YourTinymceEditorConfigBundlePlugin = new pimcore.plugin.YourTinymceEditorConfigBundle();    

To load the editmode.js file in editmode, you need to implement getEditmodeJsPaths in your bundle class. Given your bundle is named AppAdminBundle and your editmode.js and startup.js created before was saved to src/AppAdminBundle/public/js/editmode.js and src/AppAdminBundle/public/js/startup.js:

<?php

namespace AppAdminBundle;

use Pimcore\Extension\Bundle\AbstractPimcoreBundle;

class AppAdminBundle extends AbstractPimcoreBundle
{
    public function getEditmodeJsPaths(): array
    {
        return [
            '/bundles/appadmin/js/pimcore/editmode.js'
        ];
    }
    
    public function getJsPaths()
    {
        return [
            '/bundles/appadmin/js/pimcore/startup.js'
        ];
    }
}

Registering global configuration via events

You can also add the file which should be loaded in editmode through an event listener to avoid having to implement a PimcoreBundle just for the sake of adding a file. Given you already have an App bundle and put the JS config from above to public/js/editmode.js you can create an event listener to add the path to the list of loaded files in editmode (please see Events for details on how to implement and register event listeners):

<?php

namespace App\EventListener;

use Pimcore\Event\BundleManager\PathsEvent;
use Pimcore\Bundle\AdminBundle\Event\BundleManagerEvents;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;

class EditmodeListener implements EventSubscriberInterface
{
    public static function getSubscribedEvents(): array
    {
        return [
            BundleManagerEvents::EDITMODE_JS_PATHS => 'onEditmodeJsPaths'
        ];
    }

    public function onEditmodeJsPaths(PathsEvent $event): void
    {
        $event->addPaths([
            '/bundles/app/js/pimcore/editmode.js'
        ]);
    }
}

Loading additional TinyMCE plugins that are not shipped with this bundle

You can load additional plugins that are not shipped by default with Pimcore's TinyMCE bundle.

The following example adds the plugin charmap (Note: Included since Pimcore 11.4):

1. Download a TinyMCE dist package matching the version the bundle is currently shipped with.
2. Extract the desired plugin from the TinyMCE dist package and place it in your app's or bundle's resource folder, e.g. copy js/tinymce/plugins/charmap/plugin.min.js to public/static/js/tinymce_plugins/charmap/plugin.min.js.
3. Use TinyMCE's config option external_plugins to load the plugin:

{
    // ...
    external_plugins: {
        charmap: '/static/js/tinymce_plugins/charmap/plugin.min.js',
    },
    // ...
    charmap: [/* ... */],  // plugin's configuration
}