i did not use Nordic-Zephyr, but i have run Zephyr on ESP32/STM32.

It's true that the learning curve is very step, but their idea is reasonable.

The execution is ... not that good at this moment imo. It's nearly impossible to debug device tree "macro hell", the preprocessor is not designed to debug that, and they abuse the hell out of it.

Also i'm wondering why you dont want "RTOS", in Zephyr setup, your entry point is still old boring "main" loop.