I've never been huge into social media or even blogging when that was en vogue, but I did set up a forum on my site a little over a year ago after realising how much of a black hole for technical discussion Discord has become. I use it as an easy way to document any screwball problems I run across when working with hardware and software, and occasionally people pop in and ask questions, so I'm glad I set it up.
Something I did notice is that Google recently added Discussions and forums as a metric in the Google Search Console, and forums is now an option in the More dropdown menu on Google.com.
What forum software did you use? I’m thinking about adding a forum to my site for the same reasons you gave.
How long did it take before the first user signed up and posted?
I'm using wpForo since it integrates well with my CMS. The first users showed up in the first week, mostly because I directed YouTube questions that required posting error logs and the like to the forums. It has been a good tool for helping people out.