I've built hundreds, if not thousands, of VMs in my lifetime. Whether that's an accomplishment or insanity is a discussion for another day.
Anyway, I was building an Ubuntu VM using UTM on an M1 Mac Mini (using Screen Sharing) that I hadn't ever used for virtualization before. When I tried to boot the VM, the error "Display Output is not Active" appeared in the VM window, and it just sat there. The VM seemed to be running fine, but nothing was displaying. A reboot didn't help, nor did deleting the VM and re-creating it.
I looked around online for a while, and there was a lot of head-scratching, but there didn't seem to be a true consensus on how to fix it. People did seem to coalesce around changing the Emulated Display Card, which you can see here:
After some trial and error, I eventually landed on setting the Emulated Display Card for the Ubuntu VM to virtio-gpu-pci, and magically the display started working.
Your mileage may vary depending on your situation, and you may need to use trial-and-error to find the right setting.