CAP is Asus secure header… depending on overall operations (mod/flash), mods can be done or not in CAP files or extracted bios image without CAPSULE.
Motherboards without USB BFB cant use CAP mods.
For reading: [Guide] How to flash a modded AMI UEFI BIOS - BIOS/UEFI Modding / BIOS Modding Guides and Problems - Win-Raid Forum (level1techs.com)
Explain your mod intentions on the mod needed.