Are you sure about that? I'm using the official AT&T fiber modem (Nokia white oval) and a pi.hole for DNS. I do remember needing to change a number of settings to get it to work though.
You probably want commercial displays. They'll cost a bit more, but they're also designed to run 24/7 (think the screens they use in menus, signs, etc) so they could probably last forever as a TV.
There's a whole anthology book about this written by a bunch of big and small names, the pdf is free https://machineofdeath.net/ebook