@mbvogeldenebeim out of interest, if you put the Hub 5 back into standard router mode, does the telephony provision work then?
Now the reason I ask is that for a long time, the Hub 5 while it was on a customer trial basis, had the telephony disabled anyway as it wasn’t compatible.Now I believe that fairly recently, it was enabled but I’m not sure if that is for all Hub 5 or only a select few. It is possible that with the firmware still in a test basis, it is not impossible that it may work in router mode but not in modem mode - yet.
The telephone ports on the Hub 3 and 4 definitely do work in modem mode, so presumably the 5’s will as well, but maybe not right now.