As someone who has never owned a TV and doesn’t know about this space, are there any TV manufacturers that are just a basic screen anymore?
Westinghouse makes a line of "non-smart" TVs. A few obscure Chinese brands do also.
Not really (I've looked pretty thoroughly), but I've been looking into large format gaming monitors like the 48" Asus OLED PG48UQ [0] which are essentially dumb TV panels.
I haven't finished researching yet but happy to discover this category of monitor is a thing now, with close enough to the latest display tech at reasonable prices. I've never owned a TV either and I keep getting stuck trying to buy one because they are all so horrible.
These are essentially huge TV panels, with basic TV features like a remote control for the OSD. I guess because it's what gamers want... A TV scale monitor for use as a TV without all the smart TV bits which ruin games. There are also a bunch of "Smart Monitors" in this category to be ware, including from LG. The work is in distinguishing the true large format dumb monitors from the smart TVs in disguise.
[0] https://www.trustedreviews.com/reviews/asus-rog-swift-oled-p...
Like the sibling said, you have to look at large monitors or commercial displays. But both tend to cost a lot more for similar features (due to not having ad revenue attached, I assume) or have other compromises.
The best options seems to be finding a TV that is reported to be usable without any sign-in and without internet connection. The number of models that fall in that category is getting smaller over time.