It’s hard but not impossible, as even ‘retail displays’ run an OS in the background to control input switching, image settings etc.
Honestly the best thing to do is buy whatever TV you want (we have a couple of the LG OLEDs in our household), and don’t ever plug them into your network (or WiFi). Otherwise, with updates OS and apps become sluggish, with more ads crammed in.
Instead, use a seperate media player (e.g. Apple TV if you’re already on the iOS ecosystem, Nvidia Shield or similar for Android, HTPC if you’re so inclined etc.) - they’re more powerful, arguably more secure & private, and portable between displays if/when you upgrade.
You’re not wrong, there are a number of videos from Louis Rossman (right to repair advocate) on YouTube lambasting LG for doing this very thing on their high-end G-series OLED TVs; including defaulting to opt-in to marketing and providing PIR data after an automatic update.