A vendor could display a nag screen at inopportune moments to connect the TV. As far as I know Samsung does this.

Also, some TVs have been known to scan for open networks, and use those without permission.

Do you have a source on this?

There is none. This has been asserted for years on HN but I’ve never seen a modicum of evidence for it.

I posted it in this thread (I'm GP).

I admit, I think my source was probably HN comments. I tend to trust them more than they deserve.

I did a Google, and it seems a very sketchy claim.

we have a samsung tv that is exclusively used with an apple tv and it’s seemed ok this far but i’m not sure how/if i can completely kill it trying to connect as we currently have no nearby open networks but if one pops up it’ll try and connect and i detest that

Setup an open wifi link w/ a separate router, search Amazon for travel router for devices under US$35. This may need to provide a response from an expected domain, just connect the TV and a PC to the open wifi (that isn't connected to the internet) and use Wireshark to see what domains the TV is trying to connect to. Setup the router dns to provide 400 responses to those queries, and problem solved.

Why yes, this is a ludicrous amount of technical work to expect the average consumer to do, and it is fucking disgusting that this is even a concern. I'll continue to use my 8 year old TV, I don't need 4k for something I'm watching from 8 feet away anyway.

I had to DMZ a friend's smart TV, since it was booting excessively slowly waiting for a response from the (Sony) servers, which is why I have a work around. Still, spending $35 and polluting the 2.5ghz band even more seems stupid. The TV in question had an ethernet port, but providing 400 responses on that didn't improve boot times, since it tried to find a wifi signal after that. Just stupid that a TV will be slow to turn in depending on what external servers it can contact.

Edit-stated this was an LG TV, it was a Sony.

Connect it to your network and blackhole all their traffic.

...and so, one day, the TV finds an open Wi-Fi hotspot and sends everything it has collected anyways.

Samsung's smart tag find network could now or in the future be used to exfiltrate data from their smart tvs that arent connected. Not high bandwidth, so it would have to be OCR or text to speech probably. Just like Amazon's Sidewalk network.

Better find the cellular radio and rip it out too. Or just wrap the whole device in foil.

Got any suggestions on external streamers that don’t have the same problem as a smart tv?

You'd have to assume good faith such as that the device won't connect to some insecure WiFi when one becomes available.

that is illegal in some countries.

For big corp, illegal means possible increase of costs of doing business to a value calculated in advance.

Are we sure external streamers don't do the exact same thing? Apple TV probably doesn't. But what about Chromecast, NVIDIA Shield, Roku, and Fire TV?

Kodi/libreelec doesn’t.

Can you set up your router or PiHole to block the tracking domains? There has to be list of those.

The problem is some TV related software ( like Chromecasts and i suppose Android TV / Google TV ) use hardcored DNS servers, so a DNS level filter doesn't help.

You can block port 53 (DNS) at the firewall and allow only traffic from and to the PiHole.