I see. That is a valid concern. Though it feels unfair to say that headscale is ‘made by a tailscale employee’. From what I understand, one of the main contributors of headscale was hired by tailscale, though he is not the only maintainer and does not own the repo from what I can tell. Still, Tailscale could decide to cede all support of headscale and that would likely hurt the project a lot. In the same way however nebula could decide to switch to proprietary licenses and discontinue their open source offerings.
Never connected my LG TV to the internet. I got an Nvidia Shield TV Pro hooked up to it. The default home screen got riddled with ads as well after I got it, but at least you can change it to a third party one and never have to see it again. Otherwise a cheap used Xbox Series S might also work, but is much bigger and arguably less flexible. And if you want a truly privacy-respecting device you might have to go with a Linux mini PC, though that’s much more involved to set up and many commercial streaming services won’t give you the full quality streams you are paying for.