These days even HDMI has Ethernet on it so you have to make sure your streaming box doesn't export that to the TV. Or your TV could connect to your neighbor's WiFi or maybe the TV has a 4G/5G modem in it.

Some years ago there was a paper about transmitting malicious TV signals and getting code exploitation on TVs. That could result in a hacked TV that then starts attacking your streaming box to enable networking etc.