At the time of writing, virtual desktop (VD) switching gestures use 3 fingers. We support VD grids, so there are three-finger gestures allocated for up, down, left and right. Overview uses 4 fingers (up/down) because those were still available. Those seem to be the only ones enabled by default for Plasma 6, based on a quick test. 5 fingers seems to do the same as 4 fingers.

In my opinion, this assignment seems haphazard and will make it harder to add more sensible gestures later. Consider this forum post: https://discuss.kde.org/t/any-hopes-of-getting-windows-10s-three-finger-task-switching-gesture-implemented-in-plasma-6/7578

Sure we'll eventually have a way to configure gesture assignments, but we should also think about what makes sense for a roughly intuitive default behavior, so we don't have to change it drastically after Plasma 6.0 or be stuck with something suboptimal for continuity reasons.

It doesn't have to be my suggested logic, but either way we should have a mental model of "why is this functionality assigned to this gesture" (by default, at least).

Here's my rough suggestion:
* 2-finger gestures should be focused on doing stuff within an app (obviously we can't change this)
* 3-finger gestures should be focused on actions within the current VD
* 4-finger gestures should be focused on actions spanning different VDs (the most zoomed-out level of gestures)

By that logic, I'd like to suggest a change in default gesture assignments:
* VD switching to use 4-finger gestures (up, down, left, right)
* Overview to use 3-finger pinch (to open / zoom in) and spread (to close / zoom back out).
* 4-finger pinch/spread can go directly to the VD switcher view within Overview
* 3-finger up/down/left/right is not assigned by default, reserved for future gestures such as quick window switching

But really I'd be happy with anything that's backed by some kind of logic/methodology to make things easier to memorize.