VS Code won't open more than one workspace from terminal

I recently got a new Macbook and installed VS Code on it using this command:

brew install --cask visual-studio-code

However, I'm seeing a weird issue when I try and launch VS Code from the Terminal. If I cd into a directory like ~/first-repo and then type code ., it will open that repo in a VS Code window correctly. But then if I subsequently cd into a separate directory like ~/second-repo and type code ., it will not. Instead, it will merely give focus to the existing VS Code window that shows first-repo, without actually opening second-repo at all. I did some Googling and tried setting the window.openFoldersInNewWindow option to on (in my settings.json file), but this hasn't made any difference at all. What do I need to do to ensure that typing code . will open a new window?