According to developer.nordicsemi.com/.../migration_sysbuild.html , the config variable SB_CONFIG_BOOT_SIGNATURE_KEY_FILE and SB_CONFIG_BOOT_ENCRYPTION_KEY_FILE should be absolute. However, entering an absolute path triggers the following error during build. Changing this to be
ninja: error: '.........../bootloader/mcuboot/bootloader/mcuboot/enc-ec256-pub.pem', needed by 'zephyr/autogen-enckey.c', missing and no known rule to make it
Changing this to be the relative path gives this error instead
CMake Error at ........../nrf/cmake/sysbuild/image_signing.cmake:43 (message):
west sign can't find file