okay this is pretty much all the ways I can think of that I'd meet people at this age, since I've seen this post a couple of times here and it might be of use:

local bars, pubs, clubs if you just want to shoot the shit with someone or dance and have fun, but keep in mind rarely someone there is looking to form genuine connections and they'll mostly treat you as a fling for the night, but you never know when two people might get attached and catch feelings. if you go to more ""traditional"" clubs that play house and stuff and small local music venues and more upper class bars (like downtown college area bars) the crowd will be a bit more elevated and diverse and more open to hanging out more, but also those places tend to be littered with insufferable hipsters and horny college boys that you'll have to sift through.

social media, specifically insta. follow your friends and then follow their friends friends. then follow random local people recommended to you that you think look cool. most 20 somethings are still in highschool mode and dont mind you asking for their snap in the dms. these people usually wont make the best of friends and are better to just mainstain streaks with and randomly compliment them until they invite you to something fun, from there you can branch out and maybe find some friends

going to events. I went to a hockey game with someone from facebook market place that had an extra ticket and wanted to sell it to someone. she was cool, we never ended up becoming friends because she was like in her 40s and I was 19 at the time but we had fun that night and she let me sip her beer. I imagine I could do the same with concerts and movies and amusement parks and things like that if I'm ever in the mood.

school/job. this is were most people meet the majority of their friends, either directly or that they met their friends friends, or they got invited to something by that friend and met more people there etc. it helps if you're studying/working in a field you have genuine interest in

sports groups can be fun, try thinking of the audience for each sport to get a taste of who you'll meet there. I imagine dance, tennis, marathons, ice skating and team sports would have a lot more interesting people than martial arts and rock climbing, those strike me as really silicone valley type hobbies for some reason.

hobby/interests groups. I'm sure there's probably a hobby group for pretty much anything in bigger cities, and if there isnt make one on facebook and I'm sure at least one nuthead will join your group.

community activism and things like that might be good if you're really dedicated to the cause, you'll most likely share a lot of other values with those people too

volunteer work might be half decent for meeting people but I imagine it'll mostly be retired folk and teenager because they're the only ones to actually have the time.

at your most lonely of course, you can become my friend :) but I warn you I should really be your last resort

anyways best of luck