Another APIM question... Navigation or not?

What diagnosis have you done to determine that it's the module causing the issue?
That's surprising that you don't know if you have NAV or not. If you took a pic of your center screen and posted it that would have been helpful.
NAV will only be in cars with the Premium Plus package that has the large 12" screen. That package also comes with a heated steering wheel, color contrasting interior accents and stitching, stitched console cover lid, and some other things.
If you have the standard small 4.2" screen then there's no NAV.

purplepills said:

I’ll get a picture in the morning. I checked the fuses, tried the hard reset, plus a friend had the same issue and it turned out to be the APIM. I have the GT Premium package heated seats but not the heated steering wheel. I also checked the codes.

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Is your screen 4", 8", or 12"? It's really that easy to tell.
Since you have the Premium(comes with an 8" screen) but no heated steering wheel then you don't have the Premium Plus that would come with the 12". An 8" screen which means no factory NAV in your car.
There's a good chance that it's the APIM but that's certainly not a wise decision to assume that it is without diagnosis especially at over $700. There's also apparently at least 2 optional APIM modules for cars with NAV: Sound System for 2018 Ford Mustang | TascaParts.com
You need your VIN to confirm the right module.