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.
You are just missing the syscalls.c, see atached file
look at _write function which calls the _io_putchar function, this _write function is called by printf, puts, putc ...