Under display scanner on Samsungs is so horribly bad that I'm not worried about it at all :) . I often can't unlock my S10+ in five tries after which it forces me to enter pin. And S10+ cost 1000$ on release last year. I don't use any screen protectors and I've rescanned fingers after Samsung rolled out "fixes" for the scanner. It's junk.

Zero issues with the S20. It works great; not as great as TouchID on older iPhones, as if that were still an option, but barring super wet fingers or gloves, it unlocks every time while declining the fingerprints of my other fingers and the half-dozen other people who have tried mine.