English speaking? Kinda.
The Vault (OG Fallout wiki) was alive and well and had plenty of active users - not a forum per se, but similar.
RPG Codex and other RPG forums had their dedicated sections/threads to Fallout.
Bethesda forum was active too IIRC, but it was, well, Bethesda.
Probably forgetting something too.
I can't remember if Reddit was a thing back then, but subreddits did eventually help by adding a few nails in the forum's coffin.
Outside of that, there were (are?) non-English Fallout forums. French, German etc. I think. Never used any of those, but we've had user overlap.