In order to have two separate VSCode windows open that point to the same workspace, press
CTRL+Shift+P and then search for Duplicate As Workspace in New Window. This will open a new window that is associated with the current workspace.
The thing to keep in mind is that it just DUPLICATED the existing workspace in a new window. Notice that at the top of the EXPLORER it will say UNTITLED (WORKSPACE). You can now work with two windows editing your code, but when you quit out of VSCode close the duplicate workspace first. It will ask you to save the workspace. You can tell it to close without saving.