They probably wouldn't be allowed to disable the basic functionality of the TV, at least not without marketing it as "online only TV", which wouldn't look good (your internet may fail, or you may want it in a place without internet). LG will disable your "smart features" if you refuse the EULA. But that's actually the optimistic and desired outcome.
The undesirable outcome is that they just hardcode some IPs or DNS in which case PiHole would be of no use. At best you could create a NAT port forward to redirect DNS requests to the PiHole, assuming it's not DoH.
And the worst case scenario is if they build in 5G connection and take the whole connectivity aspect out of your control.