Hello !
I've been using KDE Plasma for years across several Linux distros and the "Activity" features always felt underwhelming as it felt too similar with Virtual Desktop without bringing anything really special.
I moved to QubesOS as my daily driver for the "reasonable" security and how easy it makes compartmentalizing your digital life, and it's incredible and I have yet barely scratched the surface of the possibility with this system.
When I installed KDE Plasma in QubesOS I thought that I was missing an opportunity to merge Plasma Activities' with QubesOS compartmentalization, so I created a small daemon which synchronize your Activities with your Qubes. https://gitlab.com/qubes_user_95639/KActivityQubesd
It's far from perfect and there's a lot missing from what is still possible, but it works, and in my eyes it's a bit better than good enough.
I hope this project will inspire you and allow you to refine your workflow. 😃
I'd love having this community feedback on this, I probably missed lots of better way to achieve this goal, and contribution are welcome.
Have fun ! :)