What router do you use? Where the internet comes from is less of an issue than what type of router is in use. You may want to read the system requirements FAQ here. 

I use T-Mobile 5g home internet, I have sound from my arc and sub but not my pair of ones...

Is the ARC wired or wireless?

Which, if any, devices are wired?  Are the Ones a separate stereo pair or are they bonded as surrounds to the Arc?  Have you set any wired device to ‘Disable WiFi’ in the device settings?

Note that Sonos does not officially support networks with a mobile internet connection, but I suspect this is over concerns that the signal may be unreliable.  Given a good signal, I see no reason why this should not work as well as a landline for streamed services, and should be irrelevant for local sources.

I don’t think your problem has anything to do with being on a 5g mobile network.

Note @Ant64 - it is not your WiFi that is T-Mobile 5g, it is your internet connection that is T-Mobile 5g.