How do you stop caring? I would give nearly anything for this superpower. Even obviously completely insignificant moments that matter to no-one can stick with me for days, and some stay with me for years, bubbling up and causing anxiety or low mood out of nowhere. No amount of rational analysis or forced positive thinking seems to help.

For me it was a combination of having achieved some amount of success (physical, financial, career) and also some humbling failure.

Basically I learned I'm not so bad, and I'm not a great man either. I'm good enough. I don't hurt other people.

I like myself, and when you genuinely like yourself then other people's opinions aren't quite as important. Nearly everyone responds positively when you aren't seeking other's approval (but are still kind).

I suspect this comes with age for a lot of people. Didn't happen for me until my 30s. Losing weight and getting into shape was a huge catalyst, I highly recommend it.

You have to expect that quite a few people aren't going to like you, in any case, you just aren't compatible. After all, do you like everybody else?

I'm sure some people don't like me. But they keep it to themselves. Even if they didn't, so what? Unless I did something to hurt them, I shouldn't be upset about it.

Perhaps cognitive behavior therapy could help with your anxiety.