PS: After restoring the wanted Windows 11 state from a backup, which was faster than expected, I ensured that all settings are as mentioned by the Arch Wiki:
"Enable I/O APIC" was already checked "Enable EFI" was already checked "Enable PAE/NX" was already checked "Enable Nested VT-x/AMD-V" was already checked Processors was set to 2 CPUs. I changed it to 1 CPU. "Hyper-V" was already selected "Nested Paging" was already checked "3D Acceleration" was already disabled Apart from this I resized the vdi from "Virtual Size 740.00 GB / Actual Size 723.02 GB" to ""Virtual Size 840.00 GB". At next I started the Windows 11 guest, upgraded the guest additions and restarted the Windows 11 guest. The next step was to shutdown the Windows 11 guest. It seems to be unable to finish the shutdown, but at least the host isn't locked yet. The Window title bar shows "[Stopping]" and the Window contend is a black screen.
