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
Look in GUIConf.c for a macro GUI_NUMBYTES which STemWin uses to allocate a memory pool. Default is pretty large and you may be able to reduce that to fit in .bss (if that is the source of the problem.)