Same. It's shocking how visibly my social circle shrinks as my ability to make new friendships also diminishes. I don't know if it's a part of getting in to my mid-30s (and all my friends now making families, moving away) or the pandemic, or both, but I find myself increasingly with no one to talk to.
As a 20-something year old, trying to make friends with people that you don't know is an incredibly frustrating experience because there's a good chance that the group you're trying to join were friends since childhood. No matter who you meet at this age, it seems that there is always a group they're a part of that you need to get acceptance with before you can call it a "friendship".
This isn't to say it's straight up impossible to make individual friends or join a friend group, but attempting to make friends but being treated in a lukewarm way by their clique goes a LONG way to reinforce avoidant behavior, even without an explicit rejection. Sitting in my room and learning math is far more enjoyable than that, so that's what I'll end up doing.
Once I move away from the place all of my childhood friends are, I have no idea what's going to happen.
