@t.lamprecht I managed to connect to SPICE, but still I do have weird behaviours with mouse support. Mouse is jumpy and unpredictable, often it just goes very fast along borders and is almost unpredictable. Can it be somehow fixed/tweaked?
I think you are using the novnc web console and spice graphics. if yes this is a known problem. if you use spice graphics then you have to have the connection using the spice remoteviewer downloaded from virt-manager website and your vm guest should be running the spice client drivers and the tools.
if you are running windows in the VM you need the following. https://www.spice-space.org/download/windows/spice-guest-tools/spice-guest-tools-latest.exe
if you are running windows/linux in the client from where you are connecting to the VM - you need to have the remote-viewer - get it from http://virt-manager.org/download
now your spice console should work like a charm using the virt remote-viewer (dont use novnc console for spice graphics)
hope this helps