Host VBS Mode is automatically enabled whenever Workstation Pro is launched on a suitably capable Windows 10 (or later) host with Hyper-V enabled.

If Hyper-V is disabled, Workstation Pro operates in its traditional mode. And if Hyper-V is enabled, but the WHP feature is not sufficiently recent or not installed, Workstation Pro fails to start.
Note: WHP is not supported on the Windows Server editions. Therefore, Workstation Pro host VBS mode is not available on these editions.