The guidance was for him only due to his actions, not general rule.
CAP files are the ones accepted and used with the ASUS USB BFB feature, no other files will be correctly identified and accepted by this Asus feature.
The mod can be directly from the ASUS cap files, that user option (Optional) was to work on the Intel image outside the capsulated Asus file, his choice only, cause boards with USB BFF can be mod and flash like so (Still CAPsulated), no need to extract with UEFI tool.
You have a mboard with USB BFB feature, so use it.
EDIT: You’re lost because you followed a user thread instead and not the dedicated NVMe mod guide on this forum.