I am also considering switching from an iPhone to a fairphone (or potentially something else privacy-friendly). So far I've heard that banking apps might be a problem. Also digital identification software feels like something that might be restricted on an alternative OS or a more open device. Does unlocking the bootloader mess with these things?
I would imagine streaming services that allow downloads might be restrictive about what they run on. Many of them do allow downlods, I know Spotify, Netflix, and most audiobook apps do at least. But I really have no idea, and would be really happy to hear from somebody with experience.