Probably depends on the car + alternator, but it’s not so rare for modern gas cars to have AC outlets for backseat passengers, and the ones I’ve seen are typically rated 120-150W or so. Glancing at the power meter I have on my fridge, it uses ~110W while running and only runs ~10% of the time.
Theoretically the car probably can keep up while running, BUT
Compressor startup current may blow whatever fuse is protecting that circuit.
AND
Cars are very inefficient generators. You’d be wasting a bunch of fuel so I wouldn’t generally recommend it unless it’s an emergency.
That said, in an emergency it may be worth doing for like 20 min on / 1 hr off, so that you’re running the engine only when needed, but I’m not an expert, that’s just pure speculation.
BackOnMyBS