I posted a bit about what I did above, but I don't think I am a good person to learn from. Every single bit of my trip to now seems to be predicated on divine intervention or unbelievable luck, depending on what you believe.

One thing that I did, which I felt helped a lot, was running a board game group in Tokyo. It was not a minor endeavor in retrospect; I had to get a bigger apartment/house, I cooked, and I didn't charge money; I even paid for advertising on FB and Google. However, as a result, I met a lot of interesting people and met a lot of people from backgrounds normally wouldn't (IT of course, but media, manga/animation, caretaking, Soka Gakkai (!), politics, etc..)

However, I really did only do it to play board games, it wasn't a scheme to improve my work prospects. I didn't count the costs when doing it, since I considered them important to my mental health. This also created an organic way for me to get to know people from work better ("Hey, do you want to drop by and play some games with my friends?")

There was a book written in 1936 and it is the only one you need to read.

https://www.amazon.com/How-Win-Friends-Influence-People/dp/0...

Here us a synopsis: https://fs.blog/how-to-win-friends-and-influence-people/

All the information is timeless. Most people just re-hash stuff from it and make it sound like it is new.

I'm not the OP or the parent post's author; however, pre-covid I'd give the usual answer of just join meetups, attend in person, follow the gang to the neighborhood bar or coffee or wherever they go, make friends, birds of a feather, etc. Post-covid, that scene seems non-existent to me. Being an introvert, it was certainly not a game I understood intuitively, outside of the fact that the groups were so small in my city as to be harmless to someone like me with the social skills of a loner. FWIW though, every single gig I've had for twenty years was among friends-of-friends with a common thread, typically art, music, science (OS, PL, DB), or culture (motos, bikes, skateboards).

Start tiny.

Set a reminder to check your contact list once a week.

Message someone on there you haven't talked to in a while.

Say something nice, hello, how are you, have you seen the latest tech news?

If you make this as easy and routine as brushing your teeth, you will very soon be overflowing with people who know and like you.

Kindness, consistency, and contact are all it takes.