Tiptap is fundamentally different from TinyMCE. It is possible to add allowed elements to Tiptap, though; you will need to configure it to do so with a tiptapExtension.
However, if you need functionality from TinyMCE, and you expect your editor to act like TinyMCE, then I would suggest you keep using TinyMCE. It is still available in V15, and you will be able to install it as a package even after Umbraco removes the built-in module in V16. The author of that package is looking for testers at the moment: