Okay so that was just a test. The Nucleo board in both the Arduino IDE (if STM32Duino core 2.x is used) and hence PlatformIO which uses that core expect the Nucleo to be able to setup the clock from HSE+Bypass mode. Please look into the thread Nucleo F401RE fails to execute Clock init issue - #17 by vortex314 to check whether or not your solder bridges are set-up correctly (SB16, SB50).
Indeed. For that I would recommend: Ctrl+Shift+P → Rebuild IntelliSense. If that does not work, you might have conflictin C/C++ extensions installed in VSCode and we’d need to see the list of your installed extensions.