I joined some Discord servers for maps, webgl (I'm building a mapping application) and I created one of my own. This has mostly filled the workplace Slack void. I hop in there or mute it whenever the mood strikes.

I answer some questions on StackOverflow to fill the void of mentoring in my past jobs.

I work from coffee shops or WeWork to have the opportunity for random small talk with strangers.

I do a few running clubs, pickup soccer games or hikes from Meetup to meet and talk with new people.

I try to read and reply to comments on Hacker News.

This mostly fills my socializing needs, but I also live with my girlfriend and we're semi introverted so it might not be enough for people who lean more extrovert.