Thanks for posting this. Not that I'm going to sign up for Threads, but until I came to CoSo, I never paid attention to data sharing policies.
Better to be informed!
I check permissions on everything. Anything that wants access to my contact list, for instance, better have a clear reason for needing that or it's booted.
Permissions are granted by the specific device you download to. Some will ask you "do you want to allow this app to..."
I'm not sure how Apple does it, but I've heard it's pretty careful. If it was mine, I'd check both just to be sure, but another apple user can probably give you a better answer.