Some users have been unable to register their fingerprints after installing the latest software update for the Galaxy A50. Ironically, the update promised enhanced fingerprint scanner functionality, among other things.
https://www.notebookcheck.net/Some-Galaxy-A50-users-are-reporting-that-fingerprint-registration-was-broken-by-latest-update.442855.0.html
Your finger has to be a little bit wet, than works like a charm:p
Your finger can be damp, dry or dismembered from your body and the result will be the same: this phone won't register or read a fingerprint if you have a screen protector. It doesn't matter what kind of screen protector. It can be a standard case with a plastic cover or the finest tempered glass attached to the screen itself. It won't read you as existing.
The only alternatives are to have no screen protection at all or to forego the fingerprint biometric.
Otherwise it's a decent phone.