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.
Right click on the project in the explorer window and select "Index->Rebuild" and see if that helps.
Sometimes, the code is fine but the pre-compiled headers in the Eclipse IDE are out of date.