Hi @Abrahams_Bogere,
Unfortunately, T-Mobile’s blanket implementation of a specific CG-NAT configuration prevents ARC in its current iteration from functioning without a VPN. See this thread: T-Mobile (US) 5G Home Internet: CG-NAT Blocks ARC, Workarounds Required [Ticket In]
However, the Roon team is actively researching solutions that we hope will allow for out-of-the-box port forwarding through auto-configuration (even on networks with CG-NAT).
We’ll post updates in the thread linked above as we progress with our initiative to broaden user access to ARC.