Comment by NDlurker

Get into slacklining. Set up a slackline at a park and people will come.

If you're into music, find out what local/regional bands are in your area and where the small local venues are. Show up a little early and talk to strangers.

Rock climbing isn't for me, but my brother has made a bunch of friends at the local rock climbing gym.

Bird watching clubs are everywhere and you guys can nerd out over different camera setups.

Join a running or cycling club. I've heard the ones around here are very welcoming to people new to the sports.

Table top RPGs are fun. Your local game stores probably have one shot nights where everyone is welcome and noobs are encouraged.

Find some sort of hobby you enjoy and find others who want to nerd out over it