Is there any diagnostic text displayed on the Roon → Settings → ARC page on Roon (desktop) or Roon Remote (Android or IOS)?
How is your Roon server connected to the T-Mobile router? Ideally it will be wired.
You say you have two Orbi mesh routers. Are both of these configured to operate in ‘Access Point’ mode? If they aren’t, and your Roon server is connected to one of these, then you may have a ‘MultipleNATFound’ error in the diagnostic text displayed in Roon → Settings → ARC.
Finally, is your service the 5G broadband service in the USA? If so, I believe it, on its own, is incompatible with Roon ARC (because it uses CG-NAT). See:
Specifically, the issue is talked about in the thread at:
One solution that is mentioned is the use of the free tailscale VPN. However, there are a couple of issues with this:
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It is not officially supported and is considered tinkering - so Roon staff are unlikely to help with issues and requests for help should be made to the community in tinkering
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I believe it can only be supported if you can configure your Roon Server to use the Tailscale VPN. This precludes its use with Nucleus or ROCK systems.
Further information can be found at: