Trying to block things in this way ends up being a whack-a-mole situation, and you're also suck monitoring it forever as the vendor deploys things to bypass any blocks, or adds/changes things.

I've done it in the past though it really is an annoying thing to monitor and keep up with. I guess you can use public block lists that can take care of some of it for you.

Just a note, for the linked item I haven't change anything in 2 years and it's still working fine.

That's because it's an allow list, nothing gets through unless it's specifically towards netflix domains and addresses.

It's much easier to manage then the reverse as you noted.

Sure, it could be defeated with effort but it would be visible (updates available or ads or similar), and at that point you start investigating.

It also requires some initial effort to set up if you want anything else from the TV (say youtube or amazon prime and so on)

The way I see it, there really isn't a perfect solution for any of this: you can't just go out and buy devices that do exactly what you want them to, because vendors don't want to sell those to you (unless you're a billionaire perhaps, and willing to pay truly absurd prices for bespoke custom solutions): vendors want to make a profit, and they've found they can do that more easily these days by selling stuff to consumers at razor-thin (or below-cost even) margins, and then making money after the sale with advertising and spying. It's like the Gillette razor-and-blade model. So it's up to us (consumers, collectively) to come up with workarounds and modifications and other technological solutions and share them with each other.