There is the GitHub repo and I bet @Kroc would accept pull requests. I am not currently running a copy of NoNonsense Forum myself anymore, so I am not likely to do an update myself. Though I am more than happy to review code changes.
Not sure if there was ever official support for Nginx. The forum depends on the .htaccess file used by Apache, I think. Are you using Nginx as a reverse proxy in front of an Apache instance? If so, there should not be any problems, unless Nginx is not proxying requests correctly to Apache?
:: @Martijn added on 15 Mar ’22 · 17:55
GitHub link: https://github.com/Kroc/NoNonsenseForum/issues