Development tools for Zephyr on STM32Workbench for Zephyr: VS Code extension to set up, build, flash and debug Zephyr applications on STM32.Devicetree manager: browse, edit and visualize Zephyr devicetree, STM32CubeMX-like for Zephyr.
It did not have the correct File Association for the .cpproject and .project files. You need to go to Windows -> Preferences -> (Expand) System Workbench -> File Association -> Click Install under System Configuration