You can still Duolingo and dodge (most of) the bullshit.

Use GrapheneOS.

Install Duolingo from the Aurora store, no Google account attached.

Sandbox the app and set its permissions to disallow location, disallow pulling contacts etc.

Make your Duolingo acct with a fake name and burner email (sucks for you if you already made one with your primary email and real info).

Manually add "friends" via their Duolingo usernames.

Note that, like Facebook, your contact info could be getting shared by other users who have your real info listed in their contacts. Not much you can do about that. (In fact, you could use none of the apps on this list but your contact info is probably still getting leaked by your normie friends and acquaintances.)