Created attachment 143853 [details]
Local overrides to make tablet act as tablet. Log files from libinput and Xournal

SUMMARY
Buttons on stylus of drawing tablet, which should modify "left clicks" with the stylus into right or middle clicks, are not registered in certain apps. 

STEPS TO REPRODUCE
1. Use Parblo A640 drawing tablet. Likely anything that reports a UC-Logic A640 chipset will work the same
2. Add libinput local quirk and evdev local rules to make tablet tablet-like
3. Attempt to use stylus buttons in Xournal++

OBSERVED RESULT
Pressing stylus to tablet with buttons pressed looks the same as pressing stylus to tablet with buttons not pressed. Draws as normal with pressure sensitivity working.

libinput logs stylus buttons correctly, but Xournal++ with input logging enabled doesn't see stylus buttons pressed

EXPECTED RESULT
Xournal++ detects stylus buttons, and so can be used for e.g. erasing

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Arch Linux, kernel 5.15.2-arch1-1
KDE Plasma Version: plasma-desktop 5.23.3-1 (plasma)
KDE Frameworks Version: Unsure which package this is referring to
Qt Version: qt5-base 5.15.2+kde+r257-1

ADDITIONAL INFORMATION
What programs read, for example, right mouse clicks from the stylus is inconsistent. I can right click in Firefox and Krita, but haven't found much else.

This is basically the last thing that's preventing me from switching to Arch, KDE, and Wayland full time, so I really want to get this worked out. Please let me know what information you need and I'll try me best to get it to you.