Tablet: Disable 'Map to single monitor' checkbox leaves tablet mapped to first display
Set 'Map to single monitor' checkbox, then un-check it. Tablet still will be mapped to first display (laptop's, in my case). If you bind Switch monitor action to tablet key, it will act the same.
If you un-check and change Tracking mode from 'absolute' to 'relative' and then return it back, tablet will be correctly mapped to both monitors
Manjaro419/GNOME Shell 3.32.2/Wacom CTH-490AK