What are the differences between autopilot AIs, and what settings are they unable to be used at all in, cards they cannot use, and other restrictions? Tried searching the forum but can't seem to find a similar thread...

Wunderwaffe can play without fog. Use in Strat 1v1 type settings, not in heavy expansion maps. For heavy expansions maps, use the default AI.

Yeah but am asking more so about the technical/behavioral aspects of the AIs, not necessarily which to use.

The default AI can play all settings and I believe all cards althought not necessarily in a smart way. One technical quirk is that fog gives you against all AIs an unfair advantage since the bots can not transfer information between the turns. They can only see what has happened in the turn before but if 2 turns ago you eliminated them from an area and have deployed a certain amount of armies, they have lost that information.

I mean for many cards it says for prod 2.0 it cannot understand them (like airlifts and order priority + delay)

Only use autopilot if you have already won, or don't want to win. None of them are even coming close to challenging a competent opponent.