Oh mate, I know exactly how you feel. This is exactly the type of
tit my awful manager did in the job I stayed in for 3.5 years.
The gaslighting was something else, and it'd been going on for such a long time before I could identify what was going on - I just thought I'd suddenly become terrible at every. single. little. thing.
Eventually and after a particularly identifiable and undeniable example of her being unreasonable, I found the page on the organisation's intranet about harassment & bullying, how that's defined in the workplace, and who to speak to. It was actually Occupational Health, I think, and the information was that in before reporting issues with harassment/bullying to OH,
all you had to do was speak to your line manager and they would contact OH on your behalf. This piece of
tit manager WAS my line manager!! It was a very lonely and isolating feeling knowing that the only part of the organisation that might have helped was inaccessible to me, with this
witch standing in the way. I tried my luck and emailed the OH team to ask what route was in place for reporting harassment & bullying when the person in question was the line manager I'd need to support my report. The response was basically "thanks for your email, to report instances of harassment/ bullying, you'll need to speak to your line manager who will approach us for help on your behalf".
That's when I really knew I was done there.
Standard advice with these things was to track issues and keep records of instances of problematic behaviour, which you can try. What it won't capture is the constant ad insidious picking away at your sanity/ self esteem.
In addition to keeping notes about this stuff I started to pre-empt the sorts of things she's take issue with and get proof of what I'd done/ when I'd done it/ who I'd spoken to, etc etc and it was extremely validating to find that she hated that - it absolutely got her goat that she would question something I'd done and I'd immediately be able to produce something like a screenshot/ receipt/ whatever to counter her. She knew I was onto her and she hated it. Recommended.
I also raised the issues with colleagues and supportive managers who were fantastic and did whatever they could to get me out of there. They started noticing it then, which was very reassuring. That's not available to everyone, but something to consider.
I hope you can get out soon. Almost anything will do - it's just not worth the toll it takes on you