I would pick things that align with your interests. Go to a museum, go to a play that has an intermission, go skiing, pick up a club sport, meetups, cooking classes, book signing, improv class, music class, fishing class, board game nights...
Everything I can get my brain interested in is a solo activity. I feel like whenever I try to even think about doing something that requires me to initiate contact with people, some unconscious part of me "resets" my thoughts and they just get stuck in a useless loop. On the rare occasion that I manage to override that and go somewhere, I am unable to engage with people even though I want to.
I don't hate interacting with people; quite the opposite in fact. I just for some unknown reason am seemingly completely incapable of initiating interaction with unfamiliar people (and even initiating anything with people I know is rare for me to do).
I would encourage you to spend time in those spaces with no intention to interact. Just go and spend time observing your thoughts and feelings. If you feel like you don't have much vocabulary for your emotions, two book I really recommend are Brene Brown's "Atlas of the Heart" [1], where a researcher names, describes, and compares the various emotions, and "The Emotion Thesaurus" [2], a writer's guide that includes a lot of description that can help with pattern-matching.
Once you have a handle on the feelings and what triggers them, I think you'll get some insight into the currently unknown reasons. I'd be you'll also have theories on how to work around it, but if not, a good therapist can help.
Lots of things to try.