Of all the forums I used to be active in, many are still active. The ones that died did so because the community died (i.e. they did not shift to Reddit and the like).

Reddit is great simply because it allowed anyone to create a community. No need to get a LAMP stack and deal with security vulnerabilities in your forum SW.

These days you have Lemmy and its ilk. Much higher barrier than the old LAMP stack, but also much superior to it. I do hope it takes off.