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.
Are you sure you are using the debug configuration? If you are using the release configuration with optimizations turned on you can't debug in C/C++ source level any more.