Apple - Duplicate keyboard input after upgrading to macOS Catalina

Do you happen to have Wacom settings/software installed? Seems that completely uninstalling all Wacom software and deleting its other files solves the issue.

Looks like doing so solved the problem for me, testing for 10 minutes and the issue doesn't occur.

Logitech settings may be a reason too.

Kudos to rakdavid.

It seems like resetting the NVRAM has solved the issue for me: https://support.apple.com/en-us/HT204063

EDIT: Seems like only temporarily... after putting my computer to sleep a few times, the issue has resurfaced. :(