Use Visual Studio 2019 and up

Output of the project is x64\Release\virtio.dll

Copy x64\Release\virtio.dll to Debuggers\x64\winext directory under WDK or EWDK location, for example to C:\Program Files (x86)\Windows Kits\10\Debuggers\x64

From windbg you can use !virtio.help to list available extension's commands

By default the extension supports netkvm driver

!virtio.cn
!virtio.hv
!virtio.mp
!virtio.query a b\*
!virtio.query a \*fea\*
!virtio.query a u64HostFeatures
!virtio.query a pPathBundles[0].txPath.!

if netkvm symbols are not loaded !virtio.findpdb