I found this, but I’m still working out the oma-uri stuff. Very much not my forte, but maybe this will help you.

This is great! Now to figure out how to do this by policy. I’ve been banging my head into so many walls during the past 2 days, trying to figure out if Mozilla has an .admx that will allow me to turn this off for devices via CSP, or via custom OMA-URI.

Spectre makes a line of dumb TVs, but I don’t think any of them are 4k. I spent about $600 on a 75" 1080p model last year.