I can't use GPS navigation on my Apple iPhone SE (2020) iOS 15.1
Cause 1 of 2: There's not adequate GPS signal
The first time your phone is to find a GPS signal on a new location, it may take several minutes. Urban agglomeration or forests may interfere with the GPS signal.
Solution: Go to a place with a clear view of the sky and wait a few minutes while your phone searches for a GPS signal.