In Magento 2.3 and greater, Magento team has changed WYSIWYG editor, instead of TinyMCE 3 Magento started use TinyMCE 4. On the picture below, you can see Magento 2.0-2.2 TinyMCE 3  editor: Default Magento TinyMCE 4 editor does not include a lot of tools for

Source: Magento 2.3 – TinyMCE 4 Toolbar / Text Color Tool Missing | Magefan