If your device has black bars on the top or bottom (letterbox effect) or you cannot move the mouse and it is locked to 1/3 or 1/4 of the screen pixels, you are experiencing an edge case issue some users have when upgrading from an older version.
If not, please try the option below.
This is pretty inconvenient and sorry in advance. But, this works for all remaining users.
Please uninstall the software using the settings menu in the duet app and then restart your machine to fully uninstall. Once done, please re-download the latest software and install it. You should be up and running!