SUMMARY
While on Wayland, Wacom tablet support via libinput (generally) cannot interact with window decorations.

* No matter if Wayland or XWayland
* No matter which window decorations (tested Breeze and Plastik)
* Qt apps always are fully un-interactive (tested Kate, Dolphin, Kontact, QtCreator)
* Clicks don't go beneath the window (meaning they don't activate anything in a window that's behind the currently active one)
* Some applications initiate dragging operation (for moving) but don't finish
    * Move mouse/touchpad after dragging with pen to verify
* For some reason, Kotatogram and I assume also Telegram (heavily custom Qt app) works perfectly
* For some reason, Nautilus (GTK) and Auryo (Electron) allow button interaction despite no dragging operation

STEPS TO REPRODUCE
1. Login to Plasma Wayland session
2. Plug tablet
3. Open any window
4. Attempt to move window via dragging the titlebar or clicking any of the buttons

OBSERVED RESULT
Window decorations are generally un-interactive.
Some windows initiate dragging operation but don't finish execution.
Some windows have interactive buttons.

EXPECTED RESULT
Window decorations are fully interactive.
All windows initiate and finish dragging operation to move window.
All windows have interactive buttons.

SOFTWARE/OS VERSIONS
Operating System: openSUSE Tumbleweed 20200823 (build from 2020-09-14)
KDE Plasma Version: 5.19.80
KDE Frameworks Version: 5.75.0
Qt Version: 5.15.1
Kernel Version: 5.8.0-1-default
OS Type: 64-bit
Processors: 4 × Intel® Core™ i5-7200U CPU @ 2.50GHz
Memory: 15.5 GiB of RAM
Graphics Processor: Mesa DRI Intel® HD Graphics 620

ADDITIONAL INFORMATION
Wacom Tablet: Intuos CTL480 Pen Small
Properly recognized via libinput list-devices

Device:           Wacom Intuos S Pad
Kernel:           /dev/input/event2
Group:            6
Seat:             seat0, default
Capabilities:     tablet-pad
Tap-to-click:     n/a
Tap-and-drag:     n/a
Tap drag lock:    n/a
Left-handed:      n/a
Nat.scrolling:    n/a
Middle emulation: n/a
Calibration:      n/a
Scroll methods:   none
Click methods:    none
Disable-w-typing: n/a
Accel profiles:   n/a
Rotation:         n/a

Device:           Wacom Intuos S Pen
Kernel:           /dev/input/event1
Group:            6
Seat:             seat0, default
Size:             152x95mm
Capabilities:     tablet 
Tap-to-click:     n/a
Tap-and-drag:     n/a
Tap drag lock:    n/a
Left-handed:      n/a
Nat.scrolling:    n/a
Middle emulation: n/a
Calibration:      n/a
Scroll methods:   none
Click methods:    none
Disable-w-typing: n/a
Accel profiles:   none
Rotation:         n/a