Currently only bootloader-specific artifacts (grub-efi or systemd-boot/gummiboot) can be deployed to EFI FAT partition when building a hddimg image. It meets usual requirements to boot an EFI system, but limits the support once we need to deploy files for other EFI application or document text files on installation media.

We need some way in some OE classes to achieve this. Note this task does't cover direct-boot with wic which should be a backend to consume whatever we deployed into hddimg dir (per my opinion). The later is tracked in:
https://bugzilla.yoctoproject.org/show_bug.cgi?id=10073

I mark this ticket to cause document change, assuming a new variable or syntax added for this feature.