When I’ve left jobs in the past, if there were coworkers I wanted to keep in touch with, I’d give them my personal email address and/or phone number and we would connect on LinkedIn. I’ve also had old coworkers add me on social media after they’ve left, but I personally don’t add coworkers on there unless we are legitimately friends outside of work.
About six years ago, I left a job that was a bad fit. A junior employee told our boss I was bullying her because I said something to her after she missed a deadline. He never bothered to ask my perspective. His “solution” was to have me CC a mid-level manager on every email I sent to the junior employee and I had to meet with HR. He was a bad boss, he kept a baseball bat in his office and took practice swings with it and brought it to meetings. I don’t think a lot of people managers receive much if any training in people management. Anyway, like you, I kept my head down and found something else. I will die on the hill that I was not the problem at that company. When I quit, I said something about knowing that the company wouldn’t be a long-term fit for me. We both knew what this really meant. Your boss sounds like a bad boss, but odds are they’re not stupid. Odds are, they’ll know why you’re leaving. In my exit interview, I declined to provide much feedback — this company had a retention problem, there was nothing I’d say that they hadn’t already heard — but did say yes or no when asked specific questions. On my last day, I went to say goodbye to my boss and thank him for the opportunity. He’d left early without a word. Try to leave on the highest note possible.
And yeah, you can try to leave a Glassdoor review if it’ll make you feel better, but “engaged employers” on that website can get the less favorable ones taken down. This happened to me with the company I mentioned, even though I left a balanced three-star review and didn’t get into the specifics of what happened.
Good luck at your next job! I hope it’s a better fit.