The best thing for DP's mental health has been going back to work. If he'd had the opportunity to wfh permanently, he'd have taken it - however, that would have meant him up all night, working when it is 'quieter', sleeping most of the day, not leaving the house, not speaking to anybody, not seeing any daylight and then starting work just as I got in the front door, only to put on a podcast or video that completely distracted him and he'd take 3 times as long to do anything (as is proven by the time he takes and the disasters involved in him cooking whilst there's other things distracting him).
But by going back to work, he's up early in the morning, walks to the office, gets daylight, fresh air, a bit of exercise, he has to make himself presentable (and even though he doesn't admit it, he feels better about himself when he's got a clean shirt, trousers and work boots on), he has human interaction all day, set breaks and then walks home again.
In fact, the difference in him between when he wasn't working at all to the last year was so marked, I told him that even if he did have the option to wfh, I thought that anything more than one day a week was such a spectacularly shit idea, I would take the router to work with me to make sure he went in.
Conversely, I'd love the chance to wfh 1-2 days a week. I definitely couldn't do any more than that, as so much of my job is directly talking to people/helping them, but sometimes it's nice to be able to get stuck into spreadsheets and lengthy documents without being interrupted five times before the first line is completed.