How do you play against the AI

I accidentally found out that if you set the battle, then selecting the Army and immediately press the "Ready" then you will start the game against the AI. But it can be done only by himself, without the participation of other players.

Evidence on the loaded screenshot

That's supposed to be a known feature

Yeah, definitely works, but honestly, it's really only good for getting used to the gameplay, testing things out. The AI is laughably easy, as it only appears to use air units, though it does appear to take it up to T2. But if you're playing in a multi-planet system, it never takes advantage of it.

The AI is indeed really easy. All you need to do is build a few fighters and you can easily shoot down all of the AI's fabricators and they're shut down.

As was stated, the AI is for testing out gameplay and features while Uber works on implementing functionality.

The latest patch now has the AI building T1 bots and sending them in a pretty continuous stream, which at least adds a bit more variety. You can still turtle and survive against it, which is a sure sign of a weak AI, but it at least adds another dimension to the game. A good build order, econ and land control still totally crushes the AI.