Is this any help?
Here is what I understand the situation is as of Sep 20, 2020
I have an Arris surfboard modem and Netgear Orbi Pro (wifi radio and router) with three WAP satellites.
I have an Arris XG1v4 master video box provided by Comcast for an LG C8 OLED TV. It works great. Unbelievable! A great pairing of 4K content with 4K OLED. Netflix, Youtube, Prime are all 4K. In addition, some new sporting events are network broadcast in 4K. There is a setting in "Devices", just set it to "Best Available" and it will automatically push out the 4K content.
I have two other 4K televisions. I have the XiD-P slave units. These are not 4K. From what I know the XiD-P communicates with the XG1v4 through a MOCA network http://www.mocaisinyourhouse.com/ using the installed coax cable. (That is why there is a MOCA filter at the cable drop to your dwelling.https://www.ppc-online.com/snlp-1gcw-moca-filter )
4K slave units require a compatible Comcast Gateway (modem, router and wifi radio in one device). Then what happens is you install an Xi6 box which communicates wirelessly over the house wifi with the XG1v4 to get content. There is also the option of "using your own equipment" but this seems to be a laggy and not widely available app on the TV like a Netflix app.
If the wifi in your house is above 50 then it should provide excellent 4K. My guess is that the coax cable in many houses ranges from high quality to garbage. If there is sufficient wifi signal strength then the odds of successful 4K distribution within the house is higher. The only wiring that counts is the wire to the master. (The rest of the house can be trash aluminum braid RG6 and not the tinned copper braid that should be installed like Belden 1694A)https://catalog.belden.com/techdata/EN/1694A_techdata.pdf
In summary, as far as I can tell, anyone can get 4K on one television with the XG1v4. But, you are out of luck in watching 4K Comcast on any other tv's unless you get the Comcast Gateway (XB7 for example)https://www.xfinity.com/support/articles/broadband-gateways-userguides in which case you can do your whole house up with satellites, tv, telephone, etc.
Beware, I could be completely wrong!