I'm a newly single mother (although TBH, ex-DP was fairly absent anyway, travelling for work, but at least when he was in the house I could leave it without the kids sometimes).
I'm coping by doing as Bex said in the second post - I set limits, I do that, and ignore anything more. I go to bed a couple of hours after the kids, but mine are a little older, so I can also stay in bed until 7 or 8 and safely leave them to it.
When they were younger when I felt I was drowning, I just stopped worrying about screen time, so I had a break. I sometimes slept with them, as whilst they fidgetted, they also slept longer if I was there, so it felt like a good trade off.
I didn't worry too much about crafts and stuff, but I did do things like put out bowls of water so they could play with their colour change toys. I did give them a bath each day just to give me a bit of a rest (in there with them - sometimes literally, but they would just play with the water on their own).
I didn't worry about feeding them the same stuff every day if they'd eat it, and I also did all the standard batch cooking, having a snack routine (breakfast, then fruit about 11, then small lunch etc - just like school really). I hoovered once a month if that, but did run a swiffer round the worst bits in my quick clean up once they were in bed. At one point, I used paper plates because I just couldn't face the dishwasher any more. If we weren't leaving the house, they could wear the same clothes multiple days to avoid washing.
Basically I short-cut the hell out of it. At 4 and 2 it's relentless.