One option is to buy a commercial signage display [bhphotovideo.com] which are still more like "dumb" displays. "
That is overkill. Just buy whatever TV you want and never connect to it a network. I bought a high-end Samsung and have been enjoying it for years. It has never been connected to a network. And no, there is no "open"/insecure WiFi network in range of the TV. So if it is collecting anything, it doesn't matter. "Smart" stuff should be separate and replaceable. I have a non-networked blueray player connected, my Linux desktop system, a TiVo, and a Roku Ultra. TiVo has no microphones or cameras. Roku has a mic only on the remote, yet no reports of that being an issue, and no cameras. Linux, well, that is, of course, safe.
I literally use my TV as a display monitor. Even sound is external, like it should be, using a nice audio/video amplifier and many great speakers for actual 5.1 surround. Not the fake crap you get with TV speakers or "sound bars".