I’m not able to connect to my music server from outside the home with Roon Arc. After some research, it seems that my Gateway does not support port forwarding because it uses CGNAT (Carrier Grade Network Address Translation). The port forwarding requests are automatically rejected when my ISP performs CG-NAT. I’m was going to start researching another ISP solution and thought I would reach out here first before I switch from a provider that has, in every other way, provided stellar service.
Have you contacted T-Mobile themselves and explained the situation. They may have a solution available (either static IP or an ip address from a non-CG-NAT pool).
I think you can try to work around this by using Tail Scale VPN, but, as for a direct fix I think it might be awhile. It has to do with the specific way Tmobile secures its traffic.