The researchers have discovered that automatic content recognition (ACR) tracking is active most of the time, even when TVs are used as “dumb” HDMI devices. In other words, the TV manufacturers are monitoring your private moments as well. There’s apparently no monitoring of streaming content in the UK, but there is in the US.
The only good news is that these TVs can seemingly be configured to disable ACR, provided the owners know this activity is taking place and are able to find the right settings. (I recently looked at the configuration of our TVs again, and understanding the various settings was far from easy.)
Would it work to block outgoing traffic at the router?
No. You need to request your Netflix video, you need to ACK the segments of it you receive and a lot more.
At the very least you’ll need to maintain a detailed whitelist of allowed domains and especially for the manufacturer some packets might he OK, like checking for updates, while others you’ll wanna block.
It’s likely a lot easier to just get a dumb screen and have the smart in a device you control.
If you block ALL traffic from it? Sure. It’s possible but more involved and requires the right hardware to block their tracking domains while leaving streaming apps working.
It’s best not to use smart TVs as well smart TVs. The apps they have are almost always slower or inferior in some way to the versions you get on streaming devices, updated less often, etc. I recommend pairing a TV with a quality streaming device like an Nvidia shield (or shield pro) or an AppleTV*. Alternatively if you want something a little cheaper in Androidtv space there is the Walmart brand Onn 4k pro.
*warning with Apple is while they’re pretty good on privacy (meh, there are no excellent choices that support streaming apps in 1080p quality) and don’t have ads their app-store is a bit more locked down. They have all the major streaming services but if you do high seas type stuff it will be more involved and difficult. Though if you have a local media collection (source your own discs or high seas) and run Plex or Jellyfin they have apps for both of those that work great as well as Infuse which usually requires a subscription unless you don’t need 4k or any proprietary audio codecs like dolby for any of your media. I personally can say I enjoy my AppleTV 4K and I think it’s a great device but I run my own media-server and have some common streaming services I pay for.