It's rough. Options limited, miserable weather, too long in the same place with the same people. In lockdown one, I had maybe one bad day in a month. Now it's one a week.
All I can do is try not to compare with others and look at what I can do for myself. I like to give myself 3 or 4 attainable tasks for each day. Nothing demanding - I'm not talking running marathons or writing novels. Ideally something for work (tends to take care of itself), something around the house and something for me / my family. So today will be work, building a snowman with my daughter (we had just about enough snow for it this morning) and winning an online poker tournament. Probably doing the laundry should have got on the list but, you know, snow. At least when I get to bed I can point to things that I've successfully completed.
But today's an OK day. There are days when 'brushed my teeth twice' makes the list as I desperately try to fill the time.
Once in a blue moon, there's a good day when I lower my standards to the point where I can tick off 5/6 activities. And not include basic personal hygiene to get there.
When I need to take a longer view, I try to remind myself that various things in the past seemed like the absolute end of the world at the time but are almost forgotten now (or at least, are now irrelevant). Therefore, one day, this will be the same. That crappy few months back in the day, nothing more. And we'll know that, in spite of everything, we just about kept it together.
Good luck!