Method to switch between group of groups of Mission Control Spaces?
As far as I understand, no such capability exist natively in macOS. Neither am I aware of any such general purpose, third-party tool which works on top of Mission Control.

While the following solution doesn't completely fulfil all your requirements, it may help to a certain extent in achieving the desired.

In such a scenario, I'd separate groups of such task-focused Spaces (1 or more desktops) by a blank Space/Desktop as shown (by blank I mean a desktop with a blank image set as the background wallpaper):



Since each desktop can be assigned a different wallpaper, you can create a custom wallpaper with largish text for the blank Desktop, indicating the group of Spaces with the custom task.



This could help you in quickly locating the desired ground after invoking Mission Control.