Thank you. I have Wacom Driver 6.3.40-2 . After backing up my settings I tried installing driver version 6.3.42-1, but it is incompatible with MacOS Mojave or Cintiq 21UX 2 (DTK-2100), which is what I have . So I am back to driver 6.3.40-2 . I may experiment with installing a few older drivers to see if there is any difference (on the chance that maybe the problem is only with driver 6.3.40-2 ?). Or maybe I need to bite the bullet and update to Big Sur ? What's the situation now with TVPaint running on Big Sur ? Have the issues been resolved ?
If Jeremy can't find anything in the source code that shows why the Flip Manual shortcut might not be working when triggered from the Wacom Express Key , I think I may give up on
using the Wacom Cintiq Express Keys and I'll find another type of programmable keypad like Butterstick mentioned by schwarzgrau or a Contour Shuttle Pro . (although I am hesitant to spend the money on yet another device , if I can possibly get the Wacom Express Keys to work properly to trigger the Flip Manual -- and what if those devices also don't work to trigger Flip Manual ? -- so I hold out hope that you can find a solution.)