After some trial and error, I finally figured out how to make the fingerprint sensor work in my S21+ phone, and I agree that it unlocks my phone very quickly. It also unlocks my apps very quickly.
What I'm finding is that I have to 'retrain' the sensor every 5 - 7 days. By 'retrain' I mean that I have to remove all my thumbprints and set them up all over again. After that, for the next 5 - 7 days, the phone's fingerprint sensor works really well, until it gradually stops recognizing my thumbs and I have to setup everything from scratch once again.
Setting up my thumbprints all over again isn't that big of a deal. It only takes 2 or 3 minutes. But it is an inconvenience to have to do it every week.
If this sounds familiar to anyone, is there something I'm missing? Could I be doing something wrong, or am I missing a setting somewhere in the phone? Why does the sensor seem to 'forget' my thumbprints? Thanks for your advice.
Attention Samsung Moderators: I have already tried all the steps listed here https://www.samsung.com/us/support/troubleshooting/TSG01200322 including the other steps after the "No, I need more help" option on the page, including the video "How to setup fingerprint security on Galaxy phones." I ask you kindly not to suggest these steps again and then mark my question 'solved.' In particular, please do not presume I have a screen protector - I do not have a screen protector. Many thanks.