Zephyr Workbench, a VSCode extension to manage Zephyr on STM32.
It enables users to easily create, develop, and debug Zephyr applications.
Main features:
Install host dependencies.
Import toolchain and SDK.
Create, configure, build and manage apps.
Debug STM32.
You can directly download it from the VSCode marketplace
For more details, visit the Zephyr Workbench
Run the ST-Link Utility and verify that the target communication mode is set to “Connect Under Reset”. My understanding is that if this option is not set for a L family device then the ST-Link can’t communicate with the target device.