This is ON Topic (testing windows Builds), but
I started to have problems with my shared foolder under VirtualBox some days ago.
So, no problemo, I send my application into a web based sharing place and download it from there on Windows (in the same machine, go figure: go to the USA instead of moving from one folder to another )
But since exe on Windows are around 25MB, this takes forever (from here) and started to bother me seriously.
Then, I recall a function in VirtualBox: Drag and Drop.
Nice ! as a test, I moved (in the wrong way) an image from Windows 10 Pro to a macOS (El Capitan) folder: it works ! (a 25MB file png !).
So I tried to copy with drag and drop my zipped application. That freezed the Windows desktop.
All I want now is to throw the whole out thru the window
How thins are working for you with VirtualBox (thatis with the last version) ?