For anyone wondering: Pixel 3 had a fingerprint sensor for unlocking the screen, but Pixel 4 removed it and replaced it with a face unlock. Regardless of whether face unlock works - sometimes it's inconvenient to position yourself for it (e.g. if you have bags in your hand, are driving, browsing/reading with phone on a surface, in bed, etc).

Some skipped Pixel 4 due to removing it. They considered fingerprint reading to be one of Pixel 3's most helpful features.

We still don't know if Pixel 5 will have it or not.