I got fired from a job because I took my already approved time off and told them I literally couldn't come in when they called me the day my PTO started, because I was already out of state.
There are still limits, even in at will and right to work states there are some protections.
Revoking approved time off after it's already started is definitely a valid reason for a wrongful termination lawsuit. Especially if you have evidence of previous bullshit.
That's why you should always get everything that seems even remotely bullshit in writing, and have your own backups.
Not telling someone why you are firing them isn't a magical lawsuit avoidance option. In a wrongful termination lawsuit, the courts take context into account specifically because of shitty companies/managers trying to hide behind exactly that.
They cannot legally fire you for any reason, though yes, they can fire you for no reason. The distinction often doesn't matter, but sometimes they're stupid enough to put the illegal reason in writing
They did have to pay unemployment, but they tried really hard to discourage me from seeking it, saying I likely wasn't even eligible for it and not to even bother filing.
Wow, that's shitty of them... Like, what do you even lose for trying? They knew they were going to have to pay up if you applied, those bastards were trying to gaslight you.