I can completely relate to your job stress. I loved my last job for the first 15 years. Then I got a new boss and had the 3 worst years of my career before I left. I hated going to work those last few years.

You're right that interviewers don't want the emotional truth of why you want a new job. Maybe a way to phrase it to an interviewer who asks why you are leaving your old job is to say its time for you to take the next step and have a different work experience where you can have the opportunity to learn something new. Then ask the interviewer a question about job development or employee engagement.
I hope things get better for you.