I switched from Nokia Sirocco 8 (fingerprint scanner on the back of the phone) to XR20 with shared power button and fingerprint scanner.
Now, almost each time I move my phone around the table, to the pocket etc., I accidentially unlock the phone. The button is placed right in the middle of the phone, people usually grab things to pick up (centre of mass). Tried unregistering my index and thumb fingers, but unlocking with fingerprint became a challenge then. Reregistered those fingers and carefully used only the orientation and narrow area of the fingertip usually used to unlock the phone. This made accidential unlocks less frequent a bit.
Another issue with this button is, it oscilates when pressed. When trying to turn off the phone it sends two or more keystrokes by accident resulting in Camera launch. I disabled Camera launch gesture (double power button tap) for the time being. But that is a regression for me.
Also, the red button is really great, but sometimes it gets pressed by accident when I am stuffing my phone in a pocket only to find it later with the flashlight on.
Reinventing how to handle this phone with care. It's ironic that such a sturdy phone has such delicate buttons.
Other than this, I am enyoing it a lot. Everything else works like a charm. My hands and pockets were afraid of the size and weight of it, but I got used to all the benefits huge screen brings. Don't need a tablet anymore. :)