You can find out why a commit was made by using "git blame" to find the commit.
It seems the mouse area was added so that:
" Also block wheel events on sliders in applet.
Without this, the value of slider gets changed but it won't change
the actual volume.
However, I think your approach works too, you're still blocking the wheel event from reaching the slider.
Seems to work.
It's disabled because the user may accidentally scroll on a touchpad when the pointer is over the volume applet, this is surprising and can be pretty nasty if you crank up the volume by accident.
Before this can go in, I'd like to ask the usability team for opinions.
Please see https://git.reviewboard.kde.org/r/125088/. I myself am against blocking it, but there is a valid reason for it.
Also, I think you can just remove the MouseArea (as Slider allows to change value with mouse wheel by default) instead of reimplementing the logic.
I know this is not a chat, but plasma-pa is needed to show default output on first place in applet and must can set it. Someone works on it, Harald? I can give a try, but i'm not pretty good with pulse and qml.
If pulse rejects the volume change when dragging the slider, the slider handle will jump from the cursor to the old value.
Also, external volume changes (eg. with global shortcut) are now delayed by the timer.