Visual Studio Code only show the content inside the directory
It appears that your Open Editors and directory Outline have been hidden. Right click on the Explorer section and see if they are disabled.
Enable them and your setup should return to normal.
VS Code has multi-root workspaces since 2017. You can go to File > Add Folder to Workspace... to add multiple directories.
You will now have an untitled workspace and you can save the workspace to keep it.
