If you haven't installed any FUSE yet:
brew tap homebrew/fuse
brew install Caskroom/cask/osxfuse
brew install qemu ext4fuse
qemu-img convert -p -O vmdk snapshot.qcow2 system.vmdk
This will take some time...- Download and register for a free licence of VMDK Mounter for Mac® OS X and install it.
- Reboot your macOS device.