Back to trying to run Ubuntu as VM...now trying to pass a GPU to it! (failing...)

Allright…so I was able to run Ubuntu 24 as a VM…it was slow as a limping turtle, so I figured besides the Spice problem, adding a GPU could be a great idea…so I´m tying. Installed an Nvidia GPU (3060 12gb), TN sees both the integrated Iris video and the Nvidia GPU, isolated the Nvidia. When I set it up like in the image below, I get this error message when I hit save. Of course I have no clue about its meaning…any ideas? And now the VM does not start anymore btw…
Thanks!
isolated gpu