My sympathies mate, I'm going through much the same thing (have been a fair bit longer though, not to worry though!) - there's thousands of us out here, which is consoling in some ways, but competition in others.
One thing I would advise - whether I'm in any such position to give it is a debate for another day - is if you've got any random skills or interests, try monetising them. It probably won't solve all your problems and make you the next Bezos, but it lets you do something you like and get paid for it - good for the self-esteem! For example, I got quite interested in houses at Uni. Now, I don't want to become a full-on estate agent, but I thought I'd look online (Fiverr, Upwork, Freelancer etc.) to see if anyone wants help with property searches. So a few times a month, in amongst all the actual job hunting, I might help some guy find a 3-bed semi in Leeds. I'll say I'll find some options for a price, look em up, put em in a document or spreadsheet, send em over. Helps someone out, breaks things up a bit, and all of a sudden you've got client management and negotiation experience, insight into a new sector, kept your research/presentation skills up-to-scratch.
Now, I don't suggest doing this exact thing...I'm a saddo who likes browsing RightMove, but maybe you play guitar? Say you'll write a riff for someone for cash. Or design a logo, or make a playlist, or do some proofreading. I've a few side-gigs, as it were, and whilst none of them are approaching enough to solve things, it's good experience and sometimes more fun than job-hunting. Someone said to me I should try making my own work, and I would wholeheartedly recommend it if the system is knocking you back. Also, there are quite a lot of jobs going around COVID, too. Try joining the National Vaccine Programme - you don't have to be a HCP or do the jabs directly, they're recruiting just logistics/admin too.
Otherwise, keep on keeping on. I hate the hectoring kind of response these things get from people with flawless CVs, six Lambos and a castle in Herefordshire, plays havoc with whatever way you're getting to grips with the situation. I posted something like you did in a pit of frustration a few months ago, and a very nice responder told me that since you are who you are, you will find success. If you're worried about it, and clever enough to do what you've done, then you've clearly got real drive and intellect. I don't know whether it's too late this year to try for PhD studentships in Physics, if you were still interested? I was getting knocked back left right and centre until recently, but now I'm through to the final round of four different graduate schemes and still to hear from more, got a PhD interview, and may apply for a Masters (in something I didn't fancy straight after my degree, but things change...see!). Until we're sorted, you just have to come up with ways of dealing with it. Location-wise, it's so up in the air I wouldn't even worry too much. If you got a job with a London office, whose to say you wouldn't still be working online from home come September? It's galling and can feel at times like a cruel trick, but things will resolve. It's the constant feeling of in-between that I hate. You can't move on because you're still in it...If someone just said, you're starting this job or this course in September, fill the time from now to then it'd be much easier - but when you're in that time, you feel like you're constantly in flux.
Hope your other problems aren't too bad, and keep it up. You're doing what you can!