FileSystemwatcher and VirtualBox-shared folder

I'm using Virtual Box V6.1.14 with Guest Additions on an Win10-64 Host hosting a Win10-64-Virtual machine.

In the Virtual-Box-Client I want a .NET-FileSystemWatcher-Object (.Net Framework 4.8) to notify when a file in some folder changes.

Im the Virtual machine this works well in case of

• a folder at a local drive
• an unc-path to some server-adress
• Host has a shared folder and the virtual machine uses it via Windows "Map network drive"

However, when I share a Folder from the host-machine via the VirtualBox-GUI-Option "Shared Folders" I cannot watch it and get a Win32Exception: "Unzulässige Funktion" (just have a german windows) with HR = -2147467259 (0x80004005)

Anyone knows what this means and more important: On what kind of folders this may happen too?

Is there a solution to that other than polling the directoy via a Timer?