If you get users' Mac 10.15 can't add files on input monitoring (Can't see + button). Please see attach png file. Please follow below steps to solve it.
1. Go to Accessibility and delete all of tablet files.
2. Go to Activity monitor in application, search “Pentablet” then force quit all of them. (You should can find 1 or 2 files.)
3. Uninstall tablet driver then reboot.
4. When goes back, please install driver until complete.
5. Open tablet setting then type PW. (Make sure you can see tablet UI.)
6. Add files on Accessibility complete.
7. Then you can see + button on input monitoring. Please add files complete. (If still can’t see + button, please unplug and plug XP-PEN product again.)