From my understanding:
As the Optus network via 4G does not provide a public IP - instead you use whats called NAT where a large volume of services share the same public IP.
As you all share the same IP, port forwarding is not available due to this.
I dont know why you keep posting those links over numerous threads.
As stated above - on Optus 4g Network you are being NAT network type and do not get a public IP - meaning no way that port forwarding will work as its not supported in the network setup.