[briandear]

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.

[xattt]

How would an aircraft be able to reliably “stream in” maps while in flight?

That argument makes no sense, other than a red herring saying “durr, glass cockpit bad”.

[HappyJoy]

They don't. Glass avionics have a charts database that's physically updated about every month