Doing some embedded C programming these days and the mixture between behavior
through config flags and code implementation feels very weird for me.

Also that I have to tell some modules through config flags how long string
parameters are:
https://developer.nordicsemi.com/nRF_Connect_SDK/doc/1.2.1/zephyr/reference/kconfig/CONFIG_AWS_IOT_CLIENT_ID_MAX_LEN.html

Wut?