Plasma 6 proposal: Disable scroll on Task Manager to switch active task
In general it's non-optimal for scrolling to trigger hidden behavior, unless that behavior is benign, does not change the entire screen contents, and seems connected to the thing you scrolled on. Scrolling over the volume icon to change the volume satisfies these criteria, while scrolling over the task manager is more borderline. Scrolling over a task manager entry by accident can change the entire screen contents in a disorienting way. I personally find this so disorienting that I've disabled the feature entirely.
This should be considered an expert feature, and hence disabled by default.