ESP32 Forum

I thought one could add custom options in sdkconfig.defaults such as:

CONFIG_THE_MEANING_OF_LIFE_IS=42

I thought this would be inserted into the two auto generated files sdkconfig and sdkconfig.h?

No. The sdkconfig.defaults simply sets default options for existing config options. For your thing to work, you'd also need to define CONFIG_THE_MEANING_OF_LIFE_IS in a Kconfig somewhere.