Temporarily allowed to save HTML value that contains restricted elements. Allowed HTML tags are: div, a, p, span, em, strong, ul, li, ol, h5, h4, h3, h2, h1, table, tbody, tr, td, th, tfoot, img, hr, figure, button, i, u, br, b
I believe that Magento will check for those no matter what option you choose. By default, Magento is just displaying a warning.
The command allows you to change the default behaviour and force or relax the restriction.
php bin/magento cms:wysiwyg:restrict y; will output : "HTML user content validation is now enforced
php bin/magento cms:wysiwyg:restrict n; will output : "HTML user content validation is now suggested
If you absolutely want to remove this warning, you would have to override the class Magento\Cms\Model\Wysiwyg\Validator with a preference for example.
Reference – https://magento.stackexchange.com/a/332878