I am in the process of doing so.

I can really relate to your naievate that by working hard your efforts would be rewarded. It's really disheartening how sociopathic and downright evil the people in charge can be. I think when you rise up through the ranks you lose your ability to be empathetic to the people your decisions affect. Otherwise how can you be a strong leader if you aren't afraid to ruin a few lives right? /s (just in case)

So rather than giving specific advice, I'm going to give you a few pieces of my situation. Feel free to browse my comment history to see the depths of a crippling burnout and career failure mid-30s.

I did about 10yrs of development before I got to a really sweet job in NYC. I got to experience the full startup ride from fun spunky group to getting acquired and strip mined for assets and personel.

I let the job become too much of my identity and I struggled to move on because of this.

I moved to a different state (USA) with less population density and more nature. I think this helped a lot. I'm also much more isolated which has caused its own problems.

I got into therapy. It took two different therapists, the first one when I told her I think I might be on the spectrum she told me "well I don't do that" and we wasted another 2 months before I missed a few appointments and things fell apart professionally. The SECOND therapist I found is absolutely amazing and the work we've done over the past 8 months is more significant than I've achieved alone in the past 10 years.

I worked a few menial jobs. I was at a pizza kitchen for a while, and I also worked at a kayak store. I felt like I was worthless, I couldn't get a technical job or any that I could get I couldn't tolerate. I cannot recommend this but sometimes you gotta do what you gotta do to pay the bills.

I worked a few contract jobs after my last big fulltime job. I have had a really bad stretch of gigs working for uninspiring and technically incompetent people. At some point the blame rests with me for not vetting these people, or at the very least politely delcining the work because it wouldn't be a professional work arrangement. You absolutely cannot talk reason into people who haven't reasoned themselves into the situation they are in.

I got a stable job with the state I live in. It pays a lot less than I'm used to but it affords me time to try to sharpen my technical spear and crawl back into the market I used to inhabit.

People will consider hiring you, but not the you right now. You might need to take time off from the job hunt and do something else. You might need to take work in a different field to get some perspective. You gotta find a job that rewards your natural behavior instead of exploiting you like your startup experience. The jobs are out there but 9/10 are smoke and mirrors bullshit liars trying to exploit you. It's a numbers game finding a reasonable employer and you just gotta be diligent in applying more and also really honest with yourself about whether THE COMPANY is up to YOUR standards not the other way around.

A big part of that last thing is self respect. You have to actually have it, you can't fake it. Cultivating the value you feel in yourself is hard and at times painful work but its the only way.

Good luck. "Where to begin" is one step after the other, dont give up. Find something that fucks you back even if you have to do it yourself with blood sweat and tears.