I assume you are specifically referring to the intense true black of OLED TVs? I upgraded earlier this year to LG G2, and I agree it’s a dramatic qualitative difference, not just an incremental upgrade in quality. It took me a while to get used to, I guess your eyes just get used to expecting a certain kind of image even if its less realistic. But now I could never go back.
If you have more than one TV, I’d strongly recommend only switching to OLED when you can afford to switch all of them. The other TV in my exercise room (a high end Samsung that’s only 3 years old) just looks awful to me now.
That’s it. My old, very old, TV died during Covid so I got a new one online mostly from reviews, not going and looking at them. I’m happy with it, so it worked.
There are many Pixar movies that fit the bill, and some have been recommended already, but I’ll recommend a slightly lesser known one: Coco, from 2017.
It’s based around the Mexican Day Of The Dead lore (so it’ll be seasonally appropriate soon) and will absolutely show you what your stuff is capable of, especially with regard to vibrant colors!
Apart from movie recommendations I would strongly recommend calibrating your new TV.
Out of the box the settings are often not ideal and, sometimes, downright bad (hit or miss…between manufacturers and models).
Ideally you use a DVD/Blu-Ray package that comes with blue filter glasses…cheap cardboard thing with cellophane “lens” (although I see many say those are not really needed). I see there are some YouTube videos that purport to do the same thing. Going through this process (may take 20 minutes…give or take) should help you dial in the best settings for the best picture in your room.
Even if you do not do all that it is still worth understanding the settings to avoid things like the Soap Opera effect which is gawd awful (although I have actually met people who say they like it…annoys me to no end…YMMV).