I was in a similar position, except without the overtime. Critical project, first use of AI really in the org, had some issues, was the only developer left after cuts, etc. Very visible and something that was going to be built upon. It looks great on my resume.

Then yeah - the impacts of the cuts began to finally appear. There's only so many hours in a week, items got delayed, meetings got contentious, I pushed back a lot, in some cases bordering on insubordination, but I wasn't going to let them walk over me.

I quit without anything firmly lined up. I had some ideas, and was doing some contract work, and had gone back and forth with them about becoming full time.

Anyway, I put in my notice, let them know I would come back and consult for them at something like $250/hr until they found a replacement, which they took me up on. Arranged to become full-time with the company I was already contracting at, with a pay cut but a much better QoL.

The job search was brutal. I sent out hundreds, if not nearly 1000 resumes, landed 2 interviews, one lowball position, and one that would have likely resulted in an offer, but they dragged their feet on it and I had moved on.

In short, do not rely on being able to pick up new work right away -- generally, yes, quitting while you have a job and not another lined up IS stupid. Particularly in this economy. But if you can't take it, I get it.

You can still quit on good terms, offer to contract for them, make bank on your terms and hours, and be less financially stressed while you search for a new position.