KDE Plasma - Adjust volume by mouse scroll on taskbar

See Panel Spacer Extended [Mouse actions/Gestures]

https://store.kde.org/p/2128047

Steps:

1. Right-click on desktop -> Enter Edit Mode
2. Add or Manager Widgets
3. Get New
4. Download New Plasma Widgets
5. Panel Spacer Extended [Mouse actions/Gestures]
6. Install
7. Add to panel and configure as below