I think all the existing answers are on the basis of creating a new Linux VM.
And if I understand you correctly, you already have a bare metal Linux install that you want to run whilst Windows is up.
This is the best search result I could find: https://forums.virtualbox.org/viewtopic.php?t=93437
It sounds like Virtualbox will indeed create a pseudo vhdx that points to a real partition, but windows is going to give you permissions drama.
The above link is out of date though, so its best viewed as info rather than guide.
Good luck.
Just one example of the lies and misinformation out there:
Smart people I know believe that we have to go Nuclear because it's the only green way to achieve baseload.
When press on what baseload is, they seem to think it's the minimum amount of power needed to keep the grid up.
Which for anyone listening in, is backwards, baseload is actually the minimum amount of load required because it's un-economical to spin old coal burners down. That's why people used to heat their water at night on the cheap, because the power HAD to go somewhere.
And these are smart people, just disinterested in the how and why of electricity generation.
They flick a switch, the lights come on.
Every 3 months they pay a bill and tut-tut about how expensive it is now "because of the green obsession".