Controversial approach, but I've had several jobs that feel like yours does OP. Each time I solved it by quitting. Didn't even have another job to go to.
Life is not supposed to feel like this, doesn't have to feel like this and experience has taught me there's always another job. Especially when you're at the dead-end part of the job market.
Take a look at your outgoings, see where you can cut back and what your bare bones essentials budget is. Then see how much you have in savings, accrued holiday you haven't yet taken (which you'll be paid for), add in your last month's salary to be paid and consider what you have lying around at home that could be sold. Work out how long you could survive for.
Then quit right after payday and instantly cut back to your proper hours and minimal effort while you work your month's notice, giving over all your time and energy to job searching.
If they query why the work isn't done, tell them you didn't have time. Don't fall for any offers to pay you overtime, they won't. You're burned out, it's a no, sorry, you can't. If they complain, let them. Daydream whilst they rant away and let it wash over you. When they ask if you're listening, tell them no, then remind them they're keeping you from your work.
If they try to grab you at lunchtime, your lunch hour starts when they finish talking to you. Look at your watch when they're done, it's 1.30pm your off to your lunch break now, bye. When they query why you're back at 2.30pm instead of 2pm, remind them you didn't go to lunch until 1.30pm. Talking about work, especially listening to your boss's complaints about you, should take place during working hours. Don't enter until your start time, go find a cafe or bus stop to sit at if you need to kill time. If they try to grab you at 5pm, you've got to dash, sorry, you've made plans, catch you tomorrow, bye! Thrown over your shoulder as you keep walking towards the exit.
It can be mildly amusing to watch them either blow a gasket or confusedly scratch their head as they try to figure out WTH to do with you. Mostly though it's just a relief to drop the corporate bullshit speak and just be yourself for once. They already hate you, that's where being nice has got you, not being particularly nice or bending over backwards for them any more isn't really going to make it any worse. What they going to do, fire you? 🤣.
Consider anything at all job wise that you think you could do and apply, maybe start a side hustle too, and register with an employment agency or two so they're looking for work for you too, both temporary or permanent. Look at Royal Mail and retail, which will currently be recruiting for Christmas staff.
There's nothing to be gained by staying where you are. It's already toxic and affecting your mental health and life. Get yourself gone and you'll feel so much better. Not least for taking a leap of faith and realising that if you're willing to work, full stop, there's always another job and the world won't cave in just because you defied society's expectations a little bit.