This. I do something similar, but instead got a laser projector. Similar price to a TV. I can either plug in my laptop or otherwise remotely cast to a plugged in stick. It just works. I get the added benefit from the projector where the screen needs to be pulled down - it's not in the view and I have to actively decide to start watching something.

I do a version of this approach. I have a 2018 model TCL TV that I do not give access to the internet (this one works without any issue, but I don't know if that is true of newer models). My TV is right next to my desktop computer, but in order to reduce noise and power, I bought a cheap Beelink mini PC and set it up with Fedora-GNOME and Kodi. Works very well for simple purposes and can easily handle light games. There are plenty of other (possibly better) solutions to this effect such as SBCs, spare laptops, or more capable mini PCs to handle some newer games. I would prefer using a computer instead of the Smart TV OS even without all of the concerns listed in the original post.

What's an example of a "giant display panel" that you can buy?