I found two settings, one for virt-manager itself and one for the vm window settings. That seems to have done the job for me with Video Virtio QXL doesn’t seem to need it but it works for that as well.
When you have Virtual Machine Manager open, click Edit → Preferences → Console. Make sure you have “Graphical console scaling” set to on “Always” and “Resize gues with window” set to “On”. That did it for me.
The other in the vm settings, click on “View” → Scale to Display". Set that on “Always” as well.
