Moahunter:
Unless I am misreading your reply I have to disagree. I currently can cast BBC from my laptop using Chrome browser with Surfshark VPN (on the laptop not router). The only extra thing I have to do is choose Cast screen and go full screen and not Cast tab. I can't do this from my smartphone because CC doesn't give me the option to choose Cast screen so it's more faffing to use mirroring but it works.
I'll just have to suck and see when I get the CC with Google TV.
If you can cast now then casting will work. What won't work is if the channel you are getting the stream from checks your ip address is in their country, in which case the CCwGTV stream needs to go through the VPN interface. In your cast you where not casting from BBC but from the desktop on your laptop which is different.