If you have dry hands, the under display fingerprint sensor can be unreliable. I went from a pixel 4 (had a pixel 2 before that) to the 7 and miss the pixel 4.
The 7 is great in all other regards but the fingerprint sensor only works like 30% of the time. Seems like it varies from person to person though - other folks report no problems with the sensor.
I’ve had the opposite experience too! I have dry fingers and my experience has been that the fingerprint sensor on the regular Pixel 7 rarely works. Incidentally, I also have trouble opening dog poop bags.
I miss the face unlock on the Pixel 4.