After a week worth of effort to get this working but HyperV though disabled, was causing issues where the CentOs VM in VirtualBox reported following during startup. VT-X also was enabled in BIOS.
00:00:08.071077 HM: HMR3Init: Falling back to raw-mode: VT-x is not available
00:00:08.136616 CPUM: SetGuestCpuIdFeature: Enabled Hypervisor Present bit
00:00:08.982281 HTT - Hyper-Threading Technology = 0 (1)
00:00:08.982309 HVP - Hypervisor Present (we're a guest) = 1 (1)
00:00:09.032906 VMSetError: Raw-mode is unavailable courtesy of Hyper-V.
00:00:09.048381 Power up failed (vrc=VERR_SUPDRV_NO_RAW_MODE_HYPER_V_ROOT, rc=E_FAIL (0X80004005))
Following PowerShell command reported True, which shouldn't be the case as HyperV is disabled using "Turn Windows features on or off", "bcdedit /set hypervisorlaunchtype off" and "PS C:\> Disable-WindowsOptionalFeature -Online -FeatureName Microsoft-Hyper-V-All"
PS C:\> (gcim Win32_ComputerSystem).HypervisorPresent
Then I came across this post and disabled Device Guard using DG_Readiness_Tool_v3.4. Hooray !! CentOS starts with no issues.