Hi @Aidan_Nolan,
Please accept my apologies for the long delay in responding here. According to other Virgin Media users, you can simply request a backend change for your Virgin Hub to prioritize IPv4. This may be available in your case - in the case of the user here, it was a simple phone call and a free account setting change. Here’s the referenced thread: Virgin Media HUB 2.0 [notes for Ireland users]
@James_Rome, unfortunately, as @ipeverywhere has mentioned above, T-Mobile 5G has implemented some inbound filtering on their residential-tier accounts that simply won’t allow for ARC to communicate with your Core. Please see this thread, where users have linked unofficial but successful workarounds: Is Roon ARC a No-Go for T-Mobile 5G Home Gateway Users? - #2 by Robert_F
Note that the team is actively researching easier workarounds for IPv6 support, so that Roon will auto-configure with IPv6 networks and certain common configurations of IPv4 tunneling with dual-stack lite. We don’t have a timeline or any details on this effort for now, but it’s a high priority to open up access to mobile playback via ARC to all our users, regardless of their internet service provider.