Just found my Windows 11 Pro Workstation with Hyper-V Role installed was taking approximately a 1 minute and 10 seconds to begin the restart, which felt like a lot longer than usual. Tested and found if I chose Shutdown it was still virtually immediate.

What was the cause?

A Ubuntu Hyper-V Guest VM that was running. I believe choosing Restart in the Windows 11 Host was another way of saying shutdown the VM gently. So a restart to took a while. While shutdown was just shutdown now.

The Ubuntu VM was set to restart if it had been running before at every boot so the VM always restarted and I got the same behaviour of slow restarts. Setting the Automatic Start Action to Nothing from "Automatically start it if it was running when the service stopped" stops the long restart of Windows 11.

After I shutdown the VM and then chose Restart the Hyper-V host restarting began taking well under a minute again.