@volanar NodeBB isn't really like older PHP apps where you extract it to a subfolder — it exists separately from your other web apps, but can be "mounted" on a specific subfolder path.
In the case of Moz, they used CloudFlare to redirect traffic going to that subfolder to the hosted NodeBB instance.
In more traditional setups, you'd use something like nginx to capture requests to that subfolder, and route them to NodeBB. So even if your forum is served on
/forum, you could still install NodeBB wherever you want (e.g.
/var/www/forum). The two (location on-disk and subfolder mounted) need not match.
So knowing that, yes, if you want to host your forum at https://example.org/projects/volanar/secret/forum/beta, you can.
Although it'd be quite a pain to type