Update: I had a breakthrough, I think. I sat here comparing the whites of my 7 plus to my 12 Pro Max. Turns out that I can duplicate the whites of the 7 plus, more or less, by reducing the "intensity" at the "color filters" in addition to moving the hue. Dropping the intensity by around 10% lets me duplicate the whites of the 7 plus -- at least, in this one environment at home. Who knows what will happen tomorrow in daylight.
Settings --> Accessibility --> Display text / size --> Color Filters "on", check "Color Tint" and move the hue/intensity sliders.
All this with True Tone and Night Shift turned off.
Strange thing about that "hue" slider: it looks like it is varying the color tone from green to magenta (like "tint" in editing programs such as Lightroom) but it has the effect of reducing the yellow bias, at least to my eye. Perhaps what I'm perceiving as yellow bias is really a green issue?
(Colors can drive you crazy!)
This afternoon I began to experiment with taking photographs in Central Park, and then comparing the colors on the screen of my 12 Pro Max to what I was seeing with my own eyes in the park. At that time the colors of the 12 Pro Max were very clearly biased to yellow and very bright green, a bizarre look, as I sadly expected. Looking at the same photographs with my 7 plus was much closer to reality, and also much more beautiful as well.
Hopefully when I test this tomorrow in the park it will all come together for the 12 Pro Max.
SO, I suggest that you start to take photographs and then fine tune the screen colors to match what you see with your own eyes. At least that will provide a somewhat objective standard. (Of course this assumes that the photographs themselves are true to reality....)