Puuh, I can redo it. But I had a Video 2-3 Years ago where I used a Feet and a Hand at the same time on the table (because one Hand needs to hold the Phone/Cam)

I loved it because its goofy flexing.

Its only possible on X11 Yet afaik because in X11 you can Manipulate XInput and create new Focus Groups to assign your devices there (move them to another group).

This already is used in Both KDE and Gnome Wayland, but only for Tablets (they get theie own Focus group like I can do it with X11 and XInput command tool, its the same but a feature that actually is default). You can also see a difference how Gnome can actually handle both inputs well at the same time, while KDE is a glitching nightmare