Updating navigation bar
Developers can basically draw rectangles on the display to reclaim touch input, and Google recommends blocking out system-gesture input around things like seek bars.
The side navigation panel has been a common UI style for Android apps, and since many implementations open with a swipe in from the side of the screen, this will be the most common action that is disrupted by the new system gestures.
I think the best solution is to try to not use a navigation drawer, which has been derided in the past as being a dumping ground for navigation with poor discoverability.
The one non-i Phone gesture is really weird: a swipe up, diagonally, from the corner of the display, will open the Google Assistant. There are a few strange edge-cases with the gesture system currently.
The one app that implements this right now is the Google I/O app, and it's pretty weird in practice.
The first swipe back gets eaten by the app drawer, and only the second switch back will actually go back.
This icon doesn't fit in the slimmer gesture bar, so now when a keyboard is open, the gesture bar actually grows to the old size, and then it has room to display the old button.
The other missing button from the new bar is Android 9 Pie's smart rotation switch, which just never shows up anymore.