> How would you block a random device on IPv6 that's generating its own IP?

If you’re referring to your TV presenting itself as a random device with a random address, you give it the WiFi info to an AP that you control which has no network connectivity at all, via vlan separation, routing rules, or just by the physical AP not being connected to any other network.

I have UniFi stuff and I created another AP on those which can’t talk to anything, and is unencrypted, and if my tv wants to use an insecure WiFi network it can try to use that one and fail because there’s no internet connectivity. I should just remove the WiFi module or antenna.