To the best of my knowledge, PlatformIO relies on the Microsoft C/C++ extension for its IntelliSense and other plugins are incompatible. So if that plugin is not available in your installation, your experience my be severaly degraded. Whether it relies on other APIs that are only available in the Microsoft version, I don’t know. It is possible to download the .vsix extension file directly from the marketplace website (“Download Extension”), but whether that works is as I said questionable.