SUMMARY Shade/Unshade window using mouse wheel on a window title bar does nothing under Wayland. STEPS TO REPRODUCE 1. Activate Shade/Unshade option on Mouse Wheel under System Settings/Window Managment/Window Behavior/Titlebar actions OBSERVED RESULT Using the mouse wheel on the titlebar does nothing under Wayland
Some more details: I noticed that the shade/unshade works with some non Qt programs, like Firefox-ESR, The GIMP. It doesn't work with Inkscape, nor LibreOffice (I have the package 'libreoffice-kf5' installed). Hope it helps!
*** This bug has been marked as a duplicate of bug 377162 ***