How to use only part of the screen?

Question

I am working on a blackberry-style keyboard attachment for any Android phone (https://github.com/Dakkaron/Fairberry).

For the next revision, I'd like the keyboard to be able to slide over the screen, so that it is roughly in the same location that the virtual keyboard would usually cover. I want to do that to get a more comfortable typing position.

But since the keyboard covers the screen, Android shouldn't use the screen area below the keyboard.

Before Android 11 I could just call wm overscan from some automation tool like Automate or Tasker. But in Android 11, they removed that.

Is there any way to achieve that?

Constraints

• Should work on Android 11+, or at least 12+
• Would be better if it doesn't require root
• Should not require a reboot, since the keyboard can slide out to reveal the whole screen
• Nav bar doesn't have to be accessible, since I can remap the functions to the phyiscal keyboard.

Things that I looked into so far:

• Keeping the virtual keyboard open even when no input is selected. I couldn't find a way to do that.
• Enlarging the navbar, so that it covers the area below the keyboard. I only found a solution that requires root and a reboot every time the navbar size changes.
• Keep split screen open. But since only the bottom app is swappable, that means, you are stuck on one app. Also doesn't work for the launcher and causes issues with many apps.