There's no fuse per se for the GPS. The navigation feature is part of the radio and relies on signals captured by the Combination Antenna (shark fin). The system description in the DT manual indicates that the Body Control Module (BCM) supplies CAN Bus signals to the GPS feature for operation of the Dead Reckoning portion of the GPS.
The first question is, do all of the other features of the radio and screen interface work properly? If they do, it looks like the BCM and antenna could be at fault. In any event I think your issue will require dealer tech. diagnostics.
Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33 gallon fuel tank, factory dual exhaust, 18” wheels. Build date: 03 June 2018. Now at: 042595 miles.