Using Linux under Win 10 host & VirtualBox but clicking on "Windows Network" does nothing
 

https://imgur.com/a/OMd1yHC

I can drag and drop, but that mostly works for a small number of files and/or small files

How can I access the Win 10 host? It appears I must make the "Windows Network" functional

If you install guest additions in Linux you can then setup a shared folder. It is basically a private Windows network between the guest and host.

By default VirtualBox configures a NAT network adapter on a guest which isolates it from the host. If you switch to a Bridged network then both will be on the same network. Browsing may or may not work but you can directly access the Windows share from the linux file browser by smb://Windows_computer_name_or_IP/share_name