Magento 2.3 - TinyMCE4 Toolbar and Plugin Configuration

UPDATE: Per Magefan's below comments, you can install this editor fix via composer. Instructions in their Github Repo.

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Original answer: Create an afterGetConfig plugin to configure Magento 2.3's TinyMCE v4.6.4 WYSIWYG editor

• My below solution adds the menubar, font color, background color, image selector, and code buttons to a "loaded" toolbar

1) Create the directory [app/code/vendor/module]: app/code/Project/Customtinymce

2) Create app/code/Project/Customtinymce/etc/di.xml:

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
        <type name="Magento\Ui\Component\Wysiwyg\ConfigInterface">
            <plugin name="project_customtinymce_config"
                    type="Project\Customtinymce\Plugin\Config"
                    sortOrder="10"/>
        </type>
</config>

3) Create app/code/Project/Customtinymce/etc/module.xml:

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
    <module name="Project_Customtinymce" setup_version="0.1.0"/>
</config>

4) Create app/code/Project/Customtinymce/registration.php

<?php
\Magento\Framework\Component\ComponentRegistrar::register(
    \Magento\Framework\Component\ComponentRegistrar::MODULE,
    'Project_Customtinymce',
    __DIR__
);

5) Create the after plugin app/code/Project/Customtinymce/Plugin/Config.php:

<?php

namespace Project\Customtinymce\Plugin;


class Config
{

 protected $activeEditor;

    public function __construct(\Magento\Ui\Block\Wysiwyg\ActiveEditor $activeEditor)
    {
        $this->activeEditor = $activeEditor;
    }

    /**
     * Return WYSIWYG configuration
     *
     * @param \Magento\Ui\Component\Wysiwyg\ConfigInterface $configInterface
     * @param \Magento\Framework\DataObject $result
     * @return \Magento\Framework\DataObject
     */
    public function afterGetConfig(
        \Magento\Ui\Component\Wysiwyg\ConfigInterface $configInterface,
        \Magento\Framework\DataObject $result
    ) {

        // Get current wysiwyg adapter's path
        $editor = $this->activeEditor->getWysiwygAdapterPath();

        // Is the current wysiwyg tinymce v4?
        if(strpos($editor,'tinymce4Adapter')){

        if (($result->getDataByPath('settings/menubar')) || ($result->getDataByPath('settings/toolbar')) || ($result->getDataByPath('settings/plugins'))){
            // do not override ui_element config (unsure if this is needed)
            return $result;
        }

        $settings = $result->getData('settings');

        if (!is_array($settings)) {
            $settings = [];
        }

        // configure tinymce settings 
        $settings['menubar'] = true;
        $settings['toolbar'] = 'undo redo | styleselect | fontsizeselect | forecolor backcolor | bold italic underline strikethrough | alignleft aligncenter alignright alignjustify | bullist numlist outdent indent | table | image | code';
        $settings['plugins'] = 'textcolor image code';

        $result->setData('settings', $settings);
        return $result;
        }
        else{ // don't make any changes if the current wysiwyg editor is not tinymce 4
            return $result;
        }
    }
}

After screenshot:

Please see TinyMCE v4 Toolbar Resources for more toolbar and plugin options.

I hope this plugin helps others! Please add your helpful feedback to improve this answer.