@Papa-Emeritux
Not related with Android 11.
I had the same issue with an UT device running Focal.
I reflashed with Noble => Fingerprint didn't work.
I flashed Android 13 without doing anything except turning on the developer mode.
Then used the installer.
Boom, the fingerprint worked.
I guess flashing Android erase the registered fingerprints.
And with preexisting fingerprints, a fresh installation of Ubuntu Touch does not work...