I am running a forum (about web technologies), and have been doing so for about 24 years (damn. I’m old). I had some spam problems, but was able to get rid of it.
It probably helps that I wrote the software myself (24 years ago there weren’t many forum software projects).
But the traffic is declining. The peak was around 2003-2005, with >500 posts per day, and is slowly declining since then with a massive drop last year (about 19 posts per day). Young people only rarely use the forum anymore, despite massive modernization efforts, and the older people slowly disappear.