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 example text color or text background and this can be inconvenient for the content manager.
You can easily solve this issue, extend the WYSIWYG tool and have more options by installing magefan/module-wysiwyg-advanced free Magento 2 extension.
After the extension installation, new options will be available for you, e.g.: text color, HTML code, undo-redo, style select, font size selector, forecolor background color, strikethrough. Example:
To install magefan/module-wysiwyg-advanced, please run the CLI commands in your Magento 2 root directory:
composer require magefan/module-wysiwyg-advanced
php bin/magento setup:upgrade
php bin/magento setup:di:compile
php bin/magento setup:static-content:deploy -f