I bought a 12 Pro on release day as well, and just wasn't happy with the display, but couldn't put my finger on what was wrong. It wasn't till I had a reason to start up my old XS Max and has the two side by side that it really showed the issue with the yellow tint on the new 12 Pro.
I took the phone back to the Apple store yesterday, and the very helpful assistant got another 12 Pro out to compare with mine, and hers was even worse. She then got another, and that was the same as mine, but neither were as good as my old XS Max. They didn't have any phones in stock to replace my 12, so I just returned it and got a refund. So back to using my old XS for the moment.
There is definitely a problem out there with new 12 Pro devices and if you have one, it is worth comparing with another phone if you can. Set the the display to Light, the same brightness level and True Tone on and the Wight will have a yellow/dirty tint to it.