I was dreading my most recent tv purchase (last fall) for exactly this reason, and ended up with TCL google tv. One can apparently setup a google tv as a dumb tv and never sign it into the internet. It acts exactly how I'd want a dumb tv to work now, simply auto uses the most recent hdmi device, or the active one if the most recent one isn't active.

It has never connected to the internet, and it never will. My long term concern is that google will eventually put cell modems in their tvs, and then using my next tv as a dumb tv will no longer be an option. For now though, this is your best bet.

You can get an off-brand Android TV and install a custom launcher like https://at4klauncher.com/

My parents bought an Amazon TV at Costco that is surprisingly responsive for being a smart TV.

Buy an AppleTV box and don't connect the TV to WiFi.

LG seems to still be somewhat agnostic.

I picked up an android TV box for $25 that works with LineageOS.

It sucks because its android, but at least its degoogled.

Edit: for a TV, I love my 30 year old Panasonic. Paid $20 for it at the Mormon goodwill. Only 720p, but has the best speakers of any TV I've owned.

Google/Android TV seems totally fine and capable as long as you use a custom launcher to eliminate all the advertising on the home screen.

Google doesn't do scummy screen spying ("ACR", Automatic Content Recognition).

LG + never log it in to the internet + an Apple TV box. The webOS UI sucks, but so do all the others apparently, and you never have to interact with it in practice if you use the Apple TV for streaming.

I was leery of of Tizen on my Samsung TV but it's fine