What are some good activities for making friends?

Rock climbing isn't my thing, but I helped out today taking some pictures at one and wow... there are a lot of people at those. People need belayers and it just had a generally friendly atmosphere. Plus you get exercise. If I was in need of friends and liked rock climbing, I'd definitely be going there more often.

I have bouldered for a few years and will agree with the friendly atmosphere.
The closest gym is farther away than I want to drive regularly, but Rick climbing gyms always have the most friendly, chill people.

Board games at a local game store. Many will have a board game night.

Tagging onto this: there's tons of games to play that have regular tournaments. I run Warhammer 40k tournaments for my local store, and while you occasionally get tryhards that are less fun, the overwhelming majority of the community just feels like a bunch of people getting together to play plastic soldiers for a day. The new Disney game Lorcana is taking off, and there's tons of different tabletop games besides just board games to try at a local store!
- Many have card games too. My local game store has both open Pokemon TCG and Magic free play nights weekly, and tournaments occasionally. They also gave me a lot of free cards and helped me in improving my deck. And this wasn’t only the employees, but other players.
  
  They also have open DnD games they run twice a week. They give you a character sheet and help you build yours, then run a game for a couple hours. Not sure, but I bet this is more rare because you have to have a good DM who is willing to help new players, run or sometimes create a campaign, and who knows how to help players get to the end when time is limited. (DnD people don’t roast me if I’m wrong, I’m not a frequent player.)
Adjacent to this is: check your local library. Ours has regular board game nights and RPG nights. I'm pretty sure they aren't actually organized by the library itself, but they use the space and the library lists them on their website and advertises the nights on the board out front.
Hmm. Might need to check out a local game store.
As well as game stores and libraries, board game associations have meetups.

We have 5 or more clubs around town. Anywhere from 20-50 people at an event, smart interesting people generally.

Gangbang

This can mean two very different activities, lol.
- Imagine showing up dressed for the wrong one!

Whatever interests you. You probably won't make any friends forcing yourself to go to events and gatherings for things that don't interest you

That's true, but I may be interested in things that I wouldn't think of by myself that they exist.

Take a class in something random that interests you. Talk to the people in the class.

Suggestions:

glass blowing
cooking
leather ~~making~~ working
pottery
painting
scuba diving

Side bonus is maybe you discover a new hobby that brings you joy.

The other ones sound reasonable, except the last. It seems like a big jump. Don't get me wrong, scuba diving is fun. I'd say go for a lesson and see if you want to continue, it may not be for you. It can also get expensive.
- Not much chatting during scuba either.
Leather making sounds interesting. Take the hide, process it. Tanning? Not sure. Gruesome and a rewarding final result.
- They probably meant leather working / crafting like making wallets and stuff.

If there is something you're passionate about, then going to events that are about that. Usually it's easier to make friends when you have something in common that you're both passionate about.

Take some sort of hobby class. Painting, woodworking, etc. Join a club of something that interests you. Play in a pool league.

If you're into history, HEMA (Historical European Martial Arts), medieval reenactment and SCA are all very approachable and friendly people. They are not cheap hobbies though.

Alternatively, board game nights and Dungeons & Dragons are cheaper and also lits of fun. Check your local board games store

Mountain biking. Especially if you have a local organization for trail management. They're almost always looking for volunteers.

You'll have the biking, being active outdoors, some hiking for trail management, typically some fund raising events, bike maintenance/repair workshops, community rides and potentially more depending on the size of the group.

Good variety of activity from solo riding to big social gatherings. And I've found it a much more chill group of people than road bikers. And it doesn't really require the super expensive $2k+ bikes some people opt for. My current ride is at about $700 all in and does everything I need it to do.

Being social. Go to bars or cafés. Engage in conversation. Insert yourself tactfully when you hear someone talking about a thing you like or know about.

Also, be aware but not overly sensitive if people don't want to continue talking to you. Be friendly, but not obnoxious. Stay cognizant of social clues.

Do you play an instrument? Do you want to? Musicians are super friendly and welcoming, if that interests you.

am go to community garden

Team sports. Play weekly then go out for food/drinks together after.

I can confirm that the 2hr badminton then 1 hr Dim Sum combo is enjoyable!

Sport –

Outdoors
Can exercise
Can talk or not talk

Sports is always great, one easy option in case people aren't to keen on running around: Disc golf is easy, cheap, and every one can play.

Couch or online video games...you can go with party games like Jack box or Co-op stuff

We found awesome people at our local gymnastics place that did adult classes

Ever play a TTRPG? Give it a try, if you live in an actual civilized place you probably have a local game store and they almost certainly host games. If you live in absolute nowhere like me you could probably find local groups online. And to be clear I'm not talking about dungeons and dragons, despite what people say the ruleset isn't new player friendly (it's complicated, the books are poorly edited, missing rules, it's expensive, etc. etc.).

Try out World (or Chronicles) of Darkness, at a base level they are easier to understand than any other ttrpg i have ever played (with lots of room to get more out there as you play) and it's got a large community (as far as niche hobbies go). Oh and it's cheap, Chronicles is best about respecting your money, but generally you only need to buy a single book (the rulebook for the creature you are playing as).

Pathfinder is also a good choice as the second most popular ttrpg and they offer their rules for free online. the second edition is simpler but it does front load a lot of information on you at once (which is a good thing, you won't have to go looking for edge case rules that don't exist). First edition is also really good, but it's more complicated and you might be less likely to find games since the second edition came out.

War gaming could also be a good way to meet people, but i don't do that as much so i have less recommendations to offer, I'm afraid.

Hiking and gym. Both communities are pretty friendly and they might even overlap. Gym, I've noticed some places you can walk in, they don't even need to check your card (I go with my friend and sometimes they don't even ask for his card).

I haven't found any I've been successful at, but the closest I've come is going to the movie theater.

Indeed, what better way to get to know someone than to sit next to them for 2.5 hours in silence
- There's also the intermission periods, you know. Have you never struck a conversation before a movie, before the second act, or while in line to get snacks or tickets? Also, some movie theaters allow talking during the movie if it's one of those smalltown theaters that plays movies from a century ago.

tennis, bit of a learning curve though

I dunno, I tried it and there were a lot of competitive assholes.
- Sounds like sports in general.
- Pickleball probably fits the original request better. Lower cost of entry, and plenty of differently-abled folks playing these days.