can't run virtualbox 6.1.4 with hyper-v

I'm running VirtualBox 6.1.4 with Hyper-V but when I try to open up a VM I get the following error:

Failed to open a session for the virtual machine vagrant_default_1583698990398_29087.

VMMR0_DO_NEM_INIT_VM failed: VERR_NEM_MISSING_KERNEL_API (VERR_NEM_MISSING_KERNEL_API).

VT-x is not available (VERR_VMX_NO_VMX).

Result Code: E_FAIL (0x80004005)
Component: ConsoleWrap
Interface: IConsole {872da645-4a9b-1727-bee2-5585105b9eed}

According to https://www.virtualbox.org/wiki/Changelog-6.0 VirtualBox 6.0.0 introduced Hyper-V support. Quoting it:

Added support for using Hyper-V as the fallback execution core on Windows host, to avoid inability to run VMs at the price of reduced performance

So what gives? Is Hyper-V supported or not?

I'm running Microsoft Windows [Version 10.0.18363.657]. Here is what "Apps & Features" says I have installed: https://pastebin.com/dJrg7yD8. Here's what "Turn Windows features on or off" says: https://pastebin.com/6RT0xeN0