Are Bots computers or humans?

Idk how this Bot thing works ik its a computer but how they talk?

Bots play the game, humans can do pretty much everything else just like on a normal Lichess account.

Can Bots play anyone or only other bots?

Bots can play anyone

This is only in lobby, right? Not in the quick select?

To my knowledge, BOTS must be challenged to a game. (I.e. by humans or other bots.)

It would not be right or fair for BOTS to issue challenges in the Lobby. (And, should this ever be "automated," the user account linked to the bot should be banned, as well as the bot.)

If BOTS can issue general challenges, they should have their own Lobby, such that either Humans, or other BOTS, can accept those challenges (automated, or manually, respectively -- other bots, or humans).

What exactly would be the purpose of bots automatically challenging other bots to play?

Irritation. Consciousness. Stupidity. (Pick a term and apply it.)

The bottom line: If there is the potential for abuse, people will find a way to not only be abusive, but also push limits. Bots very succinctly represent that (specific kind of) purpose. Any time you give someone with half a brain control over anything that can be automated -- that person will find a way to put it to good use, and then extend that to other uses (i.e. leveraging in-browser JavaScript to perform Crypto-mining computation). And then you have to set limits and throttles on what someone or something can do.

Don't get me wrong -- I love LiChess, including the ability to run a "bot" of sorts. But this whole thing could go horribly wrong, unchecked. (Of mice and men.)

Or, maybe this is all very-well planned and thought-through end-to-end, and I'm wrong.

I'm happy with being wrong. That's what makes me human.