Many contracts (at least where I live, ymmv) contains a trial period, usually the first three months. Those are not just for your employers benefit. Some things, like team fit and culture, will only become apparent after a few weeks.

That being said, 6 months is a perfectly reasonable time for an employment that you’ve found unreasonable. If I’d see something like that on a resume when I was hiring, I might ask a question about the short stay during the interview process, but an answer about mis-matched culture fit would be perfectly legit for me.