About ten years ago I used WhatsApp+ which had unheard of features like rounded profile pictures. At some point they banned me for a day, then it worked again until they banned for 3 days and after a ban of two weeks I finally gave up.
Nowadays it'd be still great if there were patches to e.g. schedule messages like Signal does, but imo there isn't much missing anymore.
You have only one UI for all text chats, no need to remember on which app you talked with your cousin and on which app you talked with your friend. All of them are in this one app.
WhatsApp was build upon XMPP protocol. You can look into XMPP clients.
Besides that WhatsApp is not the way to communicate anyway. Normies use it because it is put up on their face and considered to be widely acceptable among them, while rhey don't understand how privacy invading it is.