OK so long story short.
I bought iphone 12 pro max on launch day. Since then changed my device 4 times.
All last 3 had green tints and bad flickering and yellow tint.
Going back to apple like crazy.
Setting up again and again made me crazy.
But in the end my 4th device did the trick.
It has NO green tint or flickering and the display is much better. No yellow hue. I would say still its a bit yellowish (only a bit) than XS max but I can deal with it.
I am happy with it and will keep it now.
I still went through a lot of pain going back to apple and changing my device 4 times, setting it up 4 times.
But what ends well is all well.
Hint: If your device is green and flickers it is a hardware issue NOT software. Return it!!!
Hint: I compared 4 other display models. All were a bit yellow with my XS max. I think this could be fixed with a software update.
Flickering and green tint is hardware issue.
Good luck.