Requested Feature: Ability to port forward etc.

Their network topology upstream from the modem breaks unsolicited inbound traffic... so that needs to be addressed first.  Doesn't matter whether the hardware on our end is configured for it or not.

XLAT464/CGNAT setup works fine for solicited communications (you request outbound first, so things can be tracked/forwarded back down the route to you).

Anyone trying to reach you directly hits a "shared" public IP at the end of a sort of VPN tunnel on the perimeter, and it can't be forwarded back to you because there is no stateful path for the packets to follow back to your modem.

Those of us still on the original 4G modems have forwarding/DMZ options available in their modem... but it doesn't actually work because of how the layers on the other side are filtering/ blocking the packets.

Sure... the consoles and such would report more open NAT modes because it appears the ports get opened properly via UPnP and such... but when it comes down to it actually working in game, it fails.

DMZ doesn't work either.  Whether we connect directly to their modem or slingshot it through our own (for better wifi), doesn't matter.

The problem persists on the other side because of how the IPv4 traffic gets shunted through their IPv6 layers.

Now, if your applications were IPv6 aware and you were to connect across v6 via passthrough and such, it may behave better.

But so long as the applications are reliant on v4 without that stateful tracking angle (ie: P2P, UDP, etc., like many games use), their upstream layers will break that communication by design.

Bridge mode would be great but port forwarding is not needed these days because you can use tailscale.com which is free for personal users or pay for ngrok.  Also a less robust system like remote.it is available.  No open ports to be scanned and Tailscale is the cat's meow in mesh networking across cgnat or any firewall.  And you get a stable ip or a host name remotely to any device!