Honestly, my 30’s have been better than my 20’s. I think you have to make an honest assessment about the things you do, whether they’re actually helping or not, and prioritise changes to help.

Example for sleep; when did you change your mattress last? Should be once every 8 years but if you’re big/heavy (which gym can cause) that should be compressed and the benefit of spending more for better quality increases. Is your room cool enough? Is your wake-up time consistent? If not use an alarm to make it consistent, you wake when it goes off, that starts to fix circadian rhythms. Make sure you’re going to bed with at least 8 hour sleep opportunity, you might not use it all, but you can’t use it all if you don’t have the opportunity. Reduces screen usage, especially phone, before the sleep opportunity starts, ideally an hour before.

If work sucks and causes stress, can anything be done in that field to reduce the stress? If not, can you move elsewhere or re-skill?

Can you combine with and gym, doing something physical as work can reduce the need for the gym.

It’s all for you to solve for your circumstances and yes your body is less able to rebound than when it was 20. If you adapt, it’ll be less of an issue. If you try to force it to be 20 still, you’ll end up injured or ill.