A) albeit not visible, it was in the settings app's layouts as gesture_navigation_bar_deprecated
B) it had settings(op_gesture_button_side_enabled and others) I could manipulate through adb
What I have found out:
If you run
adb shell settings put system op_gesture_button_side_enabled 0
the back gesture gets put back to the bottom edge. However it isn't all good, as the assistant gesture stays in the corner, and the home/appswitcher gesture gets triggered a lot too, when using the back gesture.
I hope someone has an idea how to improve on this, as in its current form it is highly useless, and I wouldn't recommend it.