Always, and only use an external device for streaming services, never the software built into the TV.

Apple TV, Android TV or other devices are perfectly capable and better integrate with mobile and other devices in your network.

The tradeoff consumers are sold is trading convenience of in device apps for security.

Smart home devices like TVs, and thermostats should be treated as default hostile and isolated on a guest wireless network instead of your main one.

Use Apple TV for that.

If you want true, verifiable privacy and control, it's not an Apple TV that you need. Any old laptop or desktop computer can be used to stream content from the Internet using a Web browser or other "apps."

E.g. Netflix doesn't let you to stream 4k video in browser afaik. So no, it's not a good option.

Desktop OS also don't support Dolby Vision or fancy spatial audio formats.

Trifecta: Piracy + Local media server + Streaming device, either Apple TV/Android TV (without internet access).

No loss of quality, devices that could spy on you, don't, and those that would spy on you, can't. The only trade-off is some convenience.

It does let you do that, but only on platforms where they can enforce HDCP. So e.g. Edge on Windows or Safari on macOS work fine, and I think Chrome recently joined the list too. But not on Linux.

I.e. spend more money to do things the TV can perfectly well do. We should make the spying illegal so we can use the devices we buy to their full potential without being sold to advertisers. "Give money to this other company that may or may not also be collecting data and may also sell you out in the future" is a suboptimal solution.

I don't think we can do anything substantial. So I'm going to just use this "suboptimal" solution.

No, we should decouple the display hardware from the playback device. Spying or not, the playback part will be obsolete long before the display part.