Garmin G3X Pilot's Manual page 335

LOC Mode is activated when the automatic navigation source switch takes
place. If the AP APPR Softkey is pressed prior to the automatic navigation
source switch, LOC Mode is armed.
In the right circumstances, LOC and GS Modes can be armed while GPS
Mode is still active and the external navigator is set to GPS (not VLOC).
190-01115-00 Rev. J
GPS Navigation Mode
Automatic Transition
Aircraft Symbol Indicates Left
Turn to Track GPS Course and Descent
To Intercept Selected Altitude
Navigation Softkey
Navigation Softkeys (PFD)
Garmin G3X Pilot's Guide
Integrated Autopilot
Selected Altitude Cap-
ture Mode Automatic
Transition
315