Wacom Intuos Pro and ProPen 3 – cursor jumps to MacBook display when Photoshop is active - unusable

I am experiencing a reproducible problem with my brand new Wacom Intuos Pro M (PTK-670) and Pro Pen 3 on my MacBook with an external LG monitor.

My preferred setup is to use the external LG monitor as my main working display for Photoshop, while keeping the MacBook's built-in display available for other applications such as email, Finder or a browser.

The problem

When Photoshop is open and active, the Wacom pen correctly controls the cursor on the external LG monitor while hovering above the tablet.

However, as soon as I touch the tablet with the pen tip, the cursor immediately jumps from the external LG monitor to the MacBook's built-in display.

This can also happen simply when the pen is picked up/used while Photoshop is the active, window without me intentionally doing anything with the pen.

If I tap my Macbook screen with the pen it jumps to the LG monitor – so the pen is unusable with Photoshop.

The Wacom behaves correctly if I close the MacBook lid, leaving only the external LG monitor active.  With the MacBook closed, Photoshop and the Wacom work normally on the external monitor.

As soon as I open the MacBook again and both displays are active, the problem returns. Note that the pen behaves normally while using other software such as Finder or Lightroom Classic.  

This makes me believe the issue is specifically related to the interaction between Photoshop, the Wacom driver and the two-display configuration rather than a basic tablet or pen fault.

Troubleshooting so far

I have:

• Checked the Wacom display mapping and selected the external LG monitor.
• Checked Display Toggle settings especially on click
• Tested Force Proportion and tablet-area settings.
• Reset Photoshop preferences to their defaults. When that failed to fix anything I have completely reinstalled Photoshop so I now have a vanilla latest version 27.11.0.
• Checked/reconfigured the relevant macOS security permissions for the Wacom driver as guided by Wacom
• Restarted/shut down the Mac several times.
• Reinstalled/rechecked the Wacom software and driver permissions.
• Confirmed that the problem is associated specifically with Photoshop being the active window/application.

I have:

• Engaged with Wacom on two different occasions whose final response each time was to contact Adobe because the pen works fine except for when trying to use Photoshop.
• I have engaged with two of Adobe help desk staff whose end solution was to contact Wacom saying it was a pen problem. Both help desks simply gave up helping. 
• Ensured my Mac OS is up to date on Tahoe 27.0.1. Golden Gate
  
  I feel sure my set up is not unique and at a loss as to what to do next.  I am really really hoping someone in the community can help.
  
  Thank you
  Lesley