I'm 37 and had several relationships in my life so far, I think maybe 5 longer-term ones and many more short term casual ones.
Last one ended ~7.5 years ago. Was quite a painful breakup due to a kid being involved, I decided I didn't want a relationship for a long time and still not sure about doing it again until the right person comes along. I have the same feelings of loneliness from time to time, but it gets easier as you get older and had a few relationships that turned out to be painful.
I'm typically an introverted person at heart, but I can be extroverted. Though most of the time I prefer to spend most time alone but I have been known to be able to get out from time to time in bigger groups and "be the life of the group" but I can't sustain it like some people can.
The experience I had with dating online was quite similar, you have to do a lot of doomscrolling and going through a lot of people before you find anyone who seems interesting enough to want to date and are able to articulate themselves decently enough to match my conversation style.
The relationships I found online didn't typically last that long though, but I had some really fulfilling relationships, though a few were very toxic.
The longest relationship I had was from seeing someone in meetup (app for finding likeminded people at events) and I liked them so I found them via the event I saw them at (RSVP list) and reached out via the app. That was the "last relationship" I meant above.
Relationships were you "become a couple" take time to develop over several dates. As I say, it takes a lot of either doomscrolling or chatting to a lot of people or looking in the right places to find that person.
A lot of the time it is just searching, looking, texting, dating several people before you find someone who seems worthwhile going further with. Try to be realistic with your expectations and try not to get too many hopes up. It really isn't easy
If you go to museums and so on, do you see anyone else who seems to like the same as you? Try making a joke to them and get chatting.
You could also try reddit, some subreddits might have people who are similarly introverted and like similar things as you.