I have to use Whatsapp, unfortunately. Are there any good alternatives to the default app on Android?
I’m worried about all the data it shares with Meta. I denied all permissions but this makes it less convenient, and the app probably still sends over the data that available without them.
No.
There is no public API (nor any efforts to reverse engineer the one used by the official app afaik). WA is also client to client encrypted, meaning all your messages are only ever stored in one “main” installation of the official app, as well as in a backup file that whatsapp will put on either your google or apple cloud storage.
All the alternative apps/bridges for interacting with WA use the Whatsapp Web API to talk to your main client, which in turn talks to WA. There is no way around using the main whatsapp app, everything else still has to be used through it.
I’ve seen WA mods (basically rebuilt .apk files), but I don’t know much about them, and therefore they seem shady.