“Normal” using OEM motherboard tools method or by Flashrom?
Capsulated files are data headers with signature/security measures, exactly against modified files and used in update files from the OEM.
Flashrom doesn’t care for these and also this data is not part of the bios itself.
A dump also doesn’t contain this header.
[Guide] How to flash a modded AMI UEFI BIOS - BIOS/UEFI Modding / BIOS Modding Guides and Problems - Win-Raid Forum (level1techs.com)
EDIT:
“…but looks quite old.”
You didn’t mentioned your Asus model and the guide is not old at all, basic principles from Asus cap files and methods still valid on modern motherboards.
Good luck, all the best.