Hi, and welcome!
The navigation bar will automatically hide in certain apps/games which make use of immersive mode. When this happens, you just need to swipe from the edge of the screen where the bar should be for it to reappear. If you'd like to be able to hide the navbar on demand, you might try checking out
this thread.
What do you mean by 'dual apps'? If you're talking about splitting the screen into two so that you can run two apps side by side, just press and hold the Overview (square) button.
You might try using the
Light Flow app to customize LED notifications on a per-app basis.
The off-axis blue shift is an inherent property of the display panel used in the Pixel 2 XL. The 'fix' is to look at your phone straight on rather than tilting it to one side or the other.
Let us know what else you'd like to customize - you'll find that Android is very much 'where there's a will, there's a way' when it comes to customization.