I'm on the other side of this, in that I attend a lot of these.

I made a big effort about 12 years ago to go to a bunch of these (like three meetups a week and trying out a variety of different meetups), but now I mostly stick to a couple of them as I don't have as much time or energy for it anymore. But I've met most of my current friends through those meetups.

Find one you like and keep showing up until you're a regular, and get to know people slowly, and if they like you they start inviting you to things outside of the meetup, and then eventually you end up being friends.

I've done this with three different groups over the years and despite naturally being shy and an introvert I've ended up making friends at each one.

At the height of me doing this (like ten years ago), it got to the point where I'd go about my daily life and about once every other month I'd run into random people I've met at meetups also out and about. Like go out to dinner and spot someone I knew from a meetup also showing up to the same place, or run into them shopping at a Best Buy or something.

Meetups where you do a shared activity seems to be the best, like hikes or movies (+ dinner afterwards) or board games, since you can always focus on the activity if you don't feel like being social, and you have that activity you can always talk about as a subject.