One of the requirements to use Docker in Windows with Container Isolation is to enable Hyper-V, this is specified in the official documentation of Microsoft. (Click here if the link is dead).
If you search a lot in the internet, you'll probably find references to "Hyper-V must be enabled in the host machine", however, you might also notice that VirtualBox had a hard time integrating with Hyper-V in the past few years, i tried it myself and lost 2 days trying to figure out why i was getting blue screens all the time. As it turns out, virtualbox 6.1 was STILL having issues with Hyper-V in the host machine, so i had to turn it off in order to use my other VMs.
So i could not enable Hyper-V in the machine running Virtual