I administer a small forum dating back to 2002. It has been hosted on phpBB for many years until a migration to Discourse in 2018.
The community was unfortunately in bad shape for multiple reasons. People migrated from forums to Facebook groups, and phpBB was a prehistoric software that didnât align with the modern Internet and peopleâs habits, and wasnât smartphone-compatible.
The migration was done late, but not too late, in the sense that while the community remains small, it has a solid core of long-time users and still has new registration from time to time. So, Iâd say itâs healthy, even though most people still use Facebook groups, but also other or newers means of communication like WhatsApp or Signal.
Hereâs the average number of monthly created posts from 2002 to 2026:
Can you spot the golden era of forums? 
[edit: the forum activity was also closely tied to the sport popularity, as itâs quite niche]
You can see the activity decreasing a lot from 2016 to 2018, almost to the point of no activity, when the migration from phpBB to Discourse happened. 
The huge spike in 2020-2021 was a Discourse bug that updated all postsâ creation dates from a large single topic to the same day.
Over the last year, an average of 350 posts have been created each month.
My other community was online since 1993, using newsgroups. I think it was created by Kevin Gilbertson. If it wasnât, he was at least active on the newgroups, created the forum with vBulletin in 2001 and imported the newsgroups messages.
Which means that on our forum today, you can still read 33-year-old posts from the same community 
Then, same story as above applies. Forum turns into a derelict, bad software, no mobile view, and migration to Discourse.
Same graph as above (posts per month):
2021 was the Discourse migration. Activity decreased in 2023-2024, but never to the point of being dead, which was almost the case before the migration.
Community is healthy as well, averaging 800 posts a month. 
Both forums would be 100% dead if I had not migrated them to Discourse.
I wonât lie tho: even if those communities arenât going to disappear anytime soon, itâs a challenge to make them grow these days, where social media algorithms keep attracting people (Iâm tempted to add âsometimes against their willâ) and keep them hostage to their opaque and addictive algorithms.