Manufacturers know people do this. The TV will attempt to connect to any open network (neighbors) and I'd be shocked if they haven't at least considered packaging them with 4G/5G antennas. You're gonna need a Faraday Cage.

Well... I got lucky then: none of my 3 TVs from different brands (two of them being used as screens for computers) did this.

Provide any evidence at all that this is happening.