Newbie to TMHI...so what are we supposed to do with IPV4 devices?

Port forwarding with the T-Mobile 5G solution seems to be a bit sketchy. They don't seem to advertise what will be forwarded and what is blocked. It makes it hard to determine if the solution is viable for specific case uses. From all I have read about the behavior it does seem to come down to the 464XLAT solution which is used across their IPv6 network. The support or lack there of that is included for port forwarding seems to be rather specific. It could be the marketing profile for subscribers is narrowed down to empower them to deliver services with the lowest overhead and technical complexity. Given what they are doing is rather involved it would make sense. Will they expand services in the future? That is hard to say. Maybe if market pressure is sufficient to push for changes. 

It is not all a T-Mobile problem. It comes down in part to vendors selection for service delivery and their propensity to lean on the old tried and true technologies based upon IPv4 delivery. If more vendors would develop their services with additional support for IPv6 the migration of services for IOT based systems over IPv6 would probably be improved and simplified. Given the ports you know are needed T-Mobile support, at least escalation level, should be able to tell you for sure if they will or will not forward those ports. If they are not forwarding them a VPN solution might offer a workaround but that is at an additional cost for a personal VPN solution and a bit more to set things up.