There is a misunderstood of a lot of people about the Virtual Drive.
When you start for the first time the Nextcloud Client with Virtual drive. It creates the Whole folder/files architecture of your nextcloud account. But it download nothing. All the files are just less than 1 Kb one.
Then you can left clic on folders you want and clic on « available offline » and then the folder sync as it does normally with the legacy client.
But the more important when the first start is made, if you lose internet you are still connected to the « fake » network drive that Nextcloud created.
You can visit all the folders, and you can only interact with the files you’ve already downloaded.