Garmin glass cockpits don’t depend on Garmin services at all. Perhaps updating charts but that’s a monthly thing generally and it’s not done while airborne.
The “not FAA approved” isn’t a thing — there are devices that go in uncertified (experimental) aircraft, but those also don’t depend on live connections to Garmin services.
The “not FAA approved” isn’t a thing — there are devices that go in uncertified (experimental) aircraft, but those also don’t depend on live connections to Garmin services.