Why does VS Code underline working code in red?

Question

STM

Recently started using VS Code to write code for STM32. I put together a project for the STM32F407VG controller and everything works fine. After changing the project under STM32f103C8, all elements work the same way, compilation, uploading the firmware to the controller, debugging. The light flashes after uploading the firmware, but VSCode underlines some elements in red, as if it cannot find them, but as I understand it, the compiler is fine, because the code works, do I need to change some VS Code settings or set the paths?

Answer 1

Well, it says why it marks in red, the identifier is not defined.
But it's possible that it's actually defined, it's just that VS Code isn't smart enough to keep track of exactly where it's defined.