[SOLVED] Virtualbox very slow (VT-X not in use) after Windows 10 20H2 update

[bob1234]

I normally use Virtualbox without any problems, and it was working fine with VT-X yesterday.

Today, I ran the upgrade to Windows 10 20H2, and now when I test my Virtualbox setup, its super slow. In the bottom right it has the "turtle" icon with a V, meaning it is using native API instead of VT-X.
I am not certain how to troubleshoot this, besides what I had already checked.

I went into Turn Windows features on and off, and Hyper-V was unchecked. Just for the sake of completion, I turned it on, rebooted, turned it off, rebooted again. This did not help.
My BIOS tells me that virtualization is installed. The windows task manager says Virtualization: Enabled.

However, despite all this, Virtualbox is using native API, and basically gets stuck booting up my guest because it is so slow. Is there some new setting with the windows 10 update that I need to disable/enable?

edit: The Vbox.log has this message in it:
00:00:02.791671 CPUM: No hardware-virtualization capability detected

[bob1234]

Looks like I fixed it. Replying to myself with the answer in case anyone else gets this issue later on. I think this is preferred instead of deleting the thread?

This similar thread helped: viewtopic.php?f=1&t=62339

The additional steps I took were:
Open command line prompt as Administrator.
Run command: bcdedit /set hypervisorlaunchtype off
Shut down PC and do a cold boot(ie powered off and unplugged before turning on).

Once back up I went into my BIOS and re-verified that Intel virtualization is on, but I also turned on Intel VT-D which was previously disabled.
Once back in to windows, virtual box now has the normal computer chip V icon and not the turtle icon, and on mouseover it says VT-X enabled, and my guest boots up normally.

[DominikS]

I was pretty frustrated on Windows 11 having the same issue, I spent like 5 hours on this and suddently I stumbled on Core Isolation feature (searchable in taskbar) - I DISABLED this function and suddenly BOOM! VT-x WORKS AGAIN !!! I hope this helps someone

[kabu]

For problems with turning off green turtle our forums admins already created topic under Tutorials section:
viewtopic.php?t=99390
For others with similar issue, It is worth to check it first.