There is a nice symmetry in the fact that all apps/websites will need to take into account safe area insets to display properly on any apple device in all display modes.
If you're in desktop mode, it's reserved for the menu bar. No application can go above that line.
If you're in fullscreen mode, the screen does not render anything to pixels at or above the notched area judging by what early reviewers are saying. In other words, it all goes black and the notch "disappears," with content displaying in a rectangular area.
https://www.macrumors.com/2021/10/18/macos-hides-notch-on-ne...
The iPhone is the only Apple device where app developers need to take into account a notch and home bar safe area.
Not a big fan of the notch, but I do like consistency.
I.e., a full screen application that isn’t updated to use the notch area simply won’t, it’ll be a nice perfect rectangle.