I’m running Linux Mint on a Dell Latitude. As a teacher in a partially virtual situation, I am using a Wacom tablet (taking notes with Xournal). Since I teach in several schools as well as from home, I connect to 4 different external monitors (actually 1 projector, two TV’s and a monitor). If I mirror the laptop and external monitor, the Wacom tablet works perfectly in all four situations. If I choose not to mirror, then I can use the Graphics Tablet setting in System Settings to map the tablet to one or the other monitor. This works on all 4 monitors. However, once I have worked with the tablet mapped to one external monitor, the system will not map to a different external monitor without a reboot.
Sounds like an extremely specific situation and issue. Which Wacom product do you use exactly?
I think you need to find someone who has the exact same product as you and a similar monitor setup, as you.