Are you running the software that you want to be listening on that port while you’re doing the test? Are you sure it is actually listening on that port? You can see which ports which programs are listening on with the command sudo ss -tulpn (those options tell it to display tcp and udp listening ports and program names, and to not try to resolve IP addresses into names; see man ss for details).

If you’ve opened the port in your gateway and your local firewall and you’re running the software, it seems like it should work… one possible reason why it might not would be if you’re double NAT’d (eg the NAT gateway you’re configuring is itself behind another NAT gateway). To see if this is the case, try to find in the router’s web interface if it says what its WAN (upstream) IP address is. If it’s something else in an RFC1918 range (192.168.x, 10.x, or 172.16-31.x) then you’re double NAT’d and need to figure out how to configure the outer NAT gateway.