what are good in-person activities for making friends?

Board games. Either just standard board games and chat while you play, or something like wavelength, that's a question, or herd mentality to actually get to know people through the game.
- I'll second this. For some folks just hanging out with people can be exhausting if you're not naturally chatty. Personally, I run out of meaningful things to talk about in focused conversation pretty quickly and need a chance for my brain to "reload" or I'm stuck talking about the weather to keep a conversation going. This goes double with people I don't particularly know well.
  If you're playing a game with folks, most of the time everyone's focus is on the game or talking about things related to the game which is easy enough to do since it is a shared experience. I often find I have a whole bandolier of semi-related ideas to discuss or funny quips that build up as we play ready to be deployed at any available opportunity. That feeling of plenty in terms of conversation makes socializing over board games so much easier for me.
  
  On the other side, I notice that when I'm meeting up with friends, we sometimes get focused so much on the game, that we don't really talk anymore about things going on in our lives. Sometimes that's good, but if you are a person that finds it difficult to talk and focus on a game at the same time, it can be kinda frustrating.
- Yes, I've met a bunch of interesting people through board games, and one of them is one of my closest friends now! Facebook and Meetup are the top ways to connect, though I try to also promote the lowly, nonprofit GameNight.host whenever I can.
  Anyway, Hard to Get is another, solid cooperative discussion game: it's like Codenames, except everyone is on the same team that's trying to pare the grid down to just the 1 assassin word; the clue giver gives highly restricted, awkward/irrelevant clues about it versus all the rest.

Bank Robbery seem quite fun, I highly recommend it
- And you geht cool bonding experience for the next 5-20 years!

Join a hobby group or club for activities you’re actually interested in. It could be anything: sports, board games, video games. That way you already have a common interest with the others, and you feel less pressure to make friends because you can still spend your time doing what you enjoy.
- 100%. Also true for any craft/DIY/manual hobby activity, art (music, sketching, painting), and so on.
- This is correct, but, imo, incomplete.
  The fact is, some of these groups kind of suck. Maybe they're cliquish. Or maybe they are all dicks, or are judgemental about people who arent in the group. Or maybe they just aren't your vibe for whatever reason.
  If you are trying to make friends, I think the advise shouldn't be "join a hobby or club for something you're interested in" but "try out every hobby or club for everything you might be interested in"!
  
  Not fitting in with an existing group is a risk you take no matter which method of seeking friendship you use. Trying out new activities is always a good idea though.

Walking around in the early evening and stopping wherever people are gathering.
I was just popping out for salad greens, and ran across a group of young people having a picnic on the sidewalk. They had way too much food and were offering to share it with everyone who passed by. I wasn't hungry but I sat down and joined the picnic anyway. Great people! I stayed for over half an hour and I'm so glad I did.
And this isn't a one-off. This is how I met my wife, too, sixteen years ago. You gotta be open to spontaneous experiences.

Rock climbing, go to your local climbing gym (if you have one) and take an intro class and then go hang out once you understand the basics. It’s such a welcoming community and people are really friendly and helpful towards beginners. Gyms also have new climber nights depending on the gym and those are great chances to meet people.
- I second this. Bouldering especially since the climbs are quicker.
  
  I broke my tibia while bouldering, so be careful and warm up before you go.
- Yeah, except that it's $20 per visit. Ridiculous.
  The membership at my local is still $60/mo (and is about to increase) so it's not much better.
  
  Lots of gyms have need-based discounts, or will hire you to work, like, 2 shifts per month in return for a free membership. If you already have friends at the gym, they can often give you a guest pass. And some gyms give out free days for meetup groups, or classes that happen at the gym.
  Unfortunately, more and more we are in the age of the corporate climbing gym, where they jack up prices but brag about "diversity". The grungy old gyms where a lot of the real community building in climbing happened are slowly fading away.

Team sports

Playing pool.

That depends on what your interests and hobbies are.
- At some point though, you'll learn to like anything if that's where the friends are.
  
  I'm not sure I agree with that.

Another one I have not read in this thread yet: seek out (or organize) activities in your neighbourhood.

Volunteering or similar work, like lending a hand at small local theater or sports events. Depending on the work they might involve some downtime when you can chat with others and get to know them.

Join a choir?
- Indeed, I lead a choir and a handbell choir at the church where I work; some handbell ringers became very close friends!

Larping works great for me.

Fighting games. There's a reason the FGC still puts so much emphasis on offline play. Go to your locals, go to majors, don't just sit there playing ranked at home!

Go to meetup.com, look for subjects you're interested in, and find a local meetup to join. Can be almost anything - wine tasting, board games, gardening, whatever. Pretty much any hobby or professional interest. I met my D&D game group that way before COVID and we're still playing weekly. There are even meetups just to hang out in a group.

Great question! I use Meetup and Bumble BFF. I'm old though...
- Meetup used to be great, but seems to be enshittifying more with every passing day.
  Are there good alternatives or other ways to find groups to join?
  
  Not that I know of

Board Games!

You could try DND open play events at hobby shops.

Chess, book clubs, group running.

I've never gone to one but I have a friend that highly recommends fuck up nights (https://en.fuckupnights.com/).
Apparently it's a group that like meets up and like tells each other how they fucked up at work/in life/whatever. Kind of works like a support group but also helps to develop public speaking in a super judgement free environment.
Not totally my cup of tea but it sounds super interesting.

Libraries tend to have bulletin boards filled with upcoming community events. Plus then you're already at the library so you can grab a book or a movie or something too

Dancing. There could be many different styles - see what seems interesting for you.
Boardgame events.
Sporty/exercise events (like, walk with others from X to Y).

You're on Lemmy, so I'm assuming you're of a geeky mentality. If so, a local hackspace/hackerspace/makerspace would be a good bet.
On paper, my local one is a communal collection of tools we can all use. In practice however, it's an excellent social group for fellow weirdos. We just also have some really fun toys to use, when we need them.
https://wiki.hackerspaces.org/List_of_Hacker_Spaces
It's not fully inclusive of all of them, but a good starting point.

War (crimes) you'll be bonded for live threw trauma