Port Forwarding on Home Internet

the problem stems from the TMO side of things... even if you were able to set forwarding rules either manually or via UPnP, it won't work.

TMO is an IPv6 only network, and they chose to go the 464XLAT route for IPv4 support... which was well documented YEARS ago to break peer to peer style communications that rely on proper port traversal support.  It also compounds issues with VPN's because their tunnel functions much like a VPN itself, reducing packet size--this causes issues when you use a VPN that may be trying to use a larger packet size, which can cause fragmentation or even discarded packets.

Until they revamp their topology to properly support the dual stack environment, it will not be doable in it's "natural" state.

Can get around it somewhat with certain VPN services, but it will have it's limitations. Most only support P2P for certain known applications (like torrent software). The most flexible one I found (windscribe) that allows you to set custom forwarding rules requires an extra option for reserving your IP as well, costing upwards of $16/month depending if you subscribe on annual plans or not.