Disable toast when screen is pinned in Android

You'll need root access, a compatible Xposed framework¹ installed and EnhancedToast (an Xposed module) installed and activated in Xposed Installer app.

Once the Xposed module is activated and device rebooted, launch EnhancedToast → Android System (package name: android) → select the toasts that you want not to show up. Selection of any entry would cause its background to turn red. I sometimes need to reboot, but often, the changes take place immediately.

_{(Click an image to enlarge it)}

The command-line as well as take it or leave it approach is to do:

_{(Requires adb setup in PC; root access not required; works only in Android 5.1.x and above)}

adb shell appops set android TOAST_WINDOW deny
# this would deny all toasts from Android System

Using a terminal emulator app but with root access, do:

su

appops set android TOAST_WINDOW deny

To allow the toasts again, replace deny with allow in the said commands, as appropriate.

¹ _{Xposed Framework: Android 5.x and 6.x}