From what I can tell, Flarum in particular is super unfriendly towards no Javascript unfortunately as is Discourse. Discourse seems to at least let one view forums, even if they can't comment. We can look into filing Issue(s) with Flarum to see if the devs can improve it, but no guarantees.
There's presently nothing on the sysadmin side we can do to make the situation better. Doing a brief scan of FOSS forums, Discourse and Flarum are the only modern ones still.
