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.
Make sure that you have finished debugging with Keil or any other tool connected to the STlink.
You can retry debug then.
The error msg saying that STLink might be already in use by another tool.