Well, it is happening to me as well.
I recently purchased an iPhone 13 mini, and when I'm looking from the front is mostly ok (although the upper side and the bottom side are cooler than the mid region). When I tilt it I can see the shifting from warmer white to cooler white.
I compare it to all my LCD IPS devices and this is the first device where I suffer it. I guess it is Pentile's fault, those greenish OLED screens are maybe improved nowadays, but it's still something there.
I plan on returning it and getting another one, this time in another color, hoping to have more luck. Because if this is a pane-lottery, I want to win the price: Having a perfect screen. I think we all deserve it.
By the way... Is it there a way to look up the screen model? I've read something on the forum about it, but now I can't find the thread.