This is not Xiaomi’s fault, it’s Google’s
Gestures worked fine on MIUI 11. In the initial A12 update gestures stopped working, but you could at least circumvent it by using 3rd party gestures app like Edge Gestures. Then, a few months later Xiaomi released the update that killed even app gestures. That’s when I said fuck it, and installed a custom ROM, where gestures work with any launchers.
What’s your experience with full screen gestures and custom launchers, Pixel owners?
All phones have this. What you see as 100% is not absolute maximum capacity.