To allow both password and fingerprint authentication, allow an empty password attempt first, then prompt for the fingerprint.
Add the following to the top of /etc/pam.d/swaylock (or /etc/pam.d/sudo, or
any other file in /etc/pam.d/):
auth sufficient pam_unix.so try_first_pass likeauth nullok
auth sufficient pam_fprintd.so
Originally from https://wiki.archlinux.org/title/Fprint