Why can't I install Ubunut 20.04 (Mate) when WSL2 and Hyper-V is enabled?

[jradxl]

Why can't I install Ubunut 20.04 (Mate) when WSL2 and Hyper-V is enabled?

Windows 10 Pro, Insider, 2004, 20175.1000 VirtualBox 6.1.12 Ubuntu Mate 20.04 ISO

When the ISO boots, it runs a disk check which fails with 1 error. This error has been like this for many months now. It's not the ISO, as same ISO installs perfectly well with with VMWare Player 15.5.6

VB very nearly works - it boots to Try/Install screen. Quiting that screen allows the ISO to be "tried". But starting the Install, it fails with a read-error.

[Aren Cambre]

This seems like a forum post. It may duplicate #19987.