I have been working with VMs since 2012 and hopefully could answer your problem.
See first you might have to install VirtualBox Guest Additions on your Win10 VM. This allows you to access the shared folder on your Ubuntu host machine.
Then create a shared folder on your Ubuntu host machine. You can do this by going to VirtualBox > Settings > Shared Folders and adding a new shared folder.
Open your Win10 VM and go to Devices > Shared Folders > Shared Folders Settings
Click on the “Add” button to add a new shared folder. In the “Folder Path” field, enter the path to the shared folder on your Ubuntu host machine. In the “Folder Name” field, enter a name for the shared folder.
You can now transfer files between your Ubuntu host machine and Windows 10 virtual machine by copying and pasting them to/from the shared folder.
In short -
Launch VirtualBox, then:
—Open Devices > Shared Folders > Shared Folders Settings.
— Click +, then in Folder Path, click the arrow and select Other.
— Browse for the folder you plan to share, and click Select Folder.
— In Add Share, give the share a name you can use in both operating systems.
— Check Auto-mount and Make permanent, then OK.
From the guest OS, you'll find the share set up in the usual location for network shares.
And I think simple drag and drop would also work.
