Kind of an edge case workaround, but thought I’d share a setup that’s working well for me.
Situation: RUTM51 used as a fail-over connection for a remote leased-line. RUTM51 in passthrough mode does not provide remote GUI access so cannot remotely check on signal status, perform firmware updates etc.
Solution: connect a remote KVM (I used one from GL.iNet) to the internet-connected LAN, configured to view the hdmi output of a raspberrypi. RasPi is connected NOT to the internet-connected LAN, but just to the RUTM51 with its own fixed IP. The RasPi is obviously not remotely accessible (having no internet connection), but the KVM is. And the KVM “sees” the screen of the RasPi, to monitor the connection status and do anything else needed in the RUTM51 GUI
Even better would be if the RUTM had an HDMI out but I suspect that’s not on the development plan!