No Access to CUPS web interface

I simply cannot access the web interface for Cups no matter what I try, do I need to forward a port through the firewall?

CUPS is running on router? What error you get?

are you trying to access CUPS remotely from the internet? Of course you cannot reach it and yes, for that you either would need to portforward (which I don’t recommend) or better you should just use a VPN, and you can access more securely without exposing a port.