Hello again! I'm here too. I guess I can explain myself here.
The gestures I have on my phone now include: quickly open camera, system navigation (gesture or 2/3 button), one-handed mode, tap to check phone, lift to check phone, and prevent ringing.
From what I understand, since a gesture like this would have to be globally available, it would have to have privileged access, likely including privileged access to the hardware.
I searched online quickly and found that this gesture is available on OnePlus. There's no technical reason why it can't be included in GrapheneOS as well.
It's unlikely that GrapheneOS devs will add this functionality themselves since they're usually tied up working on other projects. So, if this gesture were to be added to GrapheneOS as an optional gesture, it would have to be implemented and supported in the future by another active contributor or a known community member.