It turns out U.S. Xperia XZ and X Compact versions' fingerprint sensors can be re-enabled
The Sony Xperia XZ has its fingerprint sensor disabled in the United States
You can still flash back the American software, though, which would restore the smartphone to a factory state. But losing your warranty is definitely something to be wary of if you are interested in modding the Xperia XZ. Should you decide to gamble, follow the instructions from this link and treat yourself to the fingerprint scanner you should have received in the first place. Reportedly, the procedure is pretty straightforward, though we haven't tried it out for ourselves – thus, proceed at your own risk!
Things that are NOT allowed: