If you use "host" please remove the nested-virt flag from the CPU to prevent VBS.can you check if VBS (virtualization based security) is running in host, and not running in x86-64-v3? i think it should be responsible for slowdown
VBS is heavily slowing down Windows VMs and can cause issues (even with the v4.
As @ucholak said, Virtualization based security. Basically a windows feature for security. Explained here: https://learn.microsoft.com/en-us/windows-hardware/design/device-experiences/oem-vbsWhat VBS ?