It works. Not well, but it works. I had a Note 9 and it was so nice to grab the phone while touching the sensor on the back, at would turn on and unlock in one quick motion. Now I have to fiddle around to power it on the Note 20, then find the right spot on the screen, and press it, and hope it works. It is reliably IF you hit the right spot.
I never understood why so many people doing reviews on the rear fingerprint readers hated them. I liked it, and the in screen reader sucks IMHO.
I have learned to tap the screen two or three times, to get the display on. Then I can locate the location to press my finger on, then hope it works. Two or three more steps then I used to have on the Note 9.