Unlock by fingerprint only When I initially set up my phone, I had to both choose a pattern and scan my fingerprint, for providing maximal security.
Now, when I want to unlock my phone, I can choose, whether I want to do that with the pattern or with my fingerprint.

Why providing the fingerprint, when someone still can use my pattern?
Is there any way, to deactivate the pattern, so that it can be unlocked by the fingerprint only?
It's not possible since FP is less secure than password/pattern. And there's another reason.

FP is stored as a "credential", which is by default, encrypted. That's why whenever you reboot your phone, or haven't unlocked your phone for 24 hours, you must unlock with pattern before you can use FP again.