oontsa hi, your forum CNAMEs to .flarum.cloud, which is now proxied as I mentioned above
According to the docs, the correct way is to CNAME to .freeflarum.com. Please, update your CNAME record to use that instead, then your forum should work
FYI this system will change in the future, as *.freeflarum.com will be proxied too and custom domains will need to be updated. But all will be announced later