Google Pixel 7a biometric unlock is not working

The checks in more detail

Go to Settings, Security and privacy, Device unlock, Face and Fingerprint Unlock and set it up again in good light, adding the glasses you wear as an alternate look. Facing the phone straight on and holding it at arm's length works best, and the setting that lets it unlock without looking at the screen can be turned off if it is too sensitive. For the fingerprint, press firmly and hold on the lit area, with a clean dry finger. A thick or air-gapped protector blocks the under-display reader, so use a compatible one or remove it to test.

Delete the prints and register again, taking in the sides and tip of the finger and registering the same finger twice. Google's guide says the same. Restart the phone and update it, as patches improve matching. If both methods fail after a drop or screen repair, hardware is at fault and needs service; if they fail together after an update, check Google's forum for known issues. Always keep a strong PIN, since biometrics fall back to it after a restart and after several failures. Back up before any repair, and if you sell the phone, remove all prints and faces first.

If you set the phone up after a software update, remember that biometrics are reset by a factory reset and must be added again, and that Google asks for the PIN after a restart or after 72 hours without an unlock. That is normal and not a fault. Practise registering the finger in the same posture you use to unlock, such as holding the phone in one hand, because the angle of the thumb on the glass differs from a flat press on a table and changes how the reader sees it.