I have the same issue recently on a S21+, it only tells me "make sure your finger covers the entire sensor" and then on the odd occasion it does sort of read I get the "press harder" error. I've tried it on my old samsung a70 with and without the same screen protector, so the problem doesn't seem to be on my fault
Last 15 days I also have the same problem with my Samsung S20 plus. I think it's an software issue. Somone should notify Samsung engineers as it's getting wide spread.
I am also having the same problem on my Samsung galaxy s20 plus. It is so frustrating. I have done factory reset twice but the problem refused to go. I love to install the monthly updates and my phone has never hit the floor. Please help. I also thought the October update will solve the problem but it still remains even after the installing the update