Well, I know some websites similar to here(I guess that’'s what your looking for?) but I don’t know how technically safe they are(so I’ll list the ones i’m pretty sure are safe):
There’s this post that was asked a months back on here: Any good free interactive sites or apps other than Choice of Games?
Also there is: https://www.playalterego.com/ (Not exactly a forum or anything but it’s a completed game.)
Since you said it doesn’t have to be free: https://itch.io/games (Not a forum but it does have Interactive fiction games on here(some are demos) but there limited.)
I think everything else has been said already.