efiboot.img is not detected as bootable

[AJIOB]

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Checklist

• [x] I looked at https://github.com/pbatard/rufus/wiki/FAQ to see if my question has already been answered.
• [x] I performed a search in the issue tracker for similar issues using keywords relevant to my problem, such as the error message I got from the log.
• [x] I clicked the 'Log' button (🗒️) or pressed Ctrl-L in Rufus, or used DebugView, and copy/pasted the log into the section that says <FULL LOG> below.
• [x] The log I am copying is the FULL log, starting with the line Rufus version: x.y.z - I have NOT removed any part of it.

Additionally (if applicable):

• [ ] I ran a bad blocks check, by clicking Show advanced format options then Check device for bad blocks, and confirmed that my USB is not defective.
• [ ] I also tried one or more of the following:
  • [ ] Using a different USB drive.
  • [ ] Plugging the USB into a different port.
  • [ ] Running Rufus on a different computer.
• [ ] If using an image, I clicked on the (✓) button to compute the MD5, SHA1 and SHA256 checksums, which are therefore present in the log I copied. I confirmed, by performing an internet search, that these values match the ones from the official image.

Issue description

I create a custom bootable UEFI ISO, based on Ubuntu manual.

I created a efiboot.img file with FAT12 & name EFI for GRUB booting.

This volume contains usual EFI/BOOT/bootx64.efi:

Zipped img file is also provided (GitHub blocks attaching pure .img files): efiboot.img.zip

Rufus doesn't detect .iso with this file .img file as bootable:

The bug is reproducable on the Rufus 4.1 & manual build for 64e85ed commit (latest for now) too.

ISO is so big to provide it here.

P.S. If I flash my ISO in dd mode - my PC can boot from it.

Log

Rufus x86 v3.20.1929
Windows version: Windows 10 Pro, 64-bit (Build 19045.3208)
Syslinux versions: 4.07/2013-07-25, 6.04/pre1
Grub versions: 0.4.6a, 2.06
System locale ID: 0x0409 (en-US)
Will use default UI locale 0x0409
SetLGP: Successfully set NoDriveTypeAutorun policy to 0x0000009E
Localization set to 'en-US'
Notice: The ISO download feature has been deactivated because 'Check for updates' is disabled in your settings.
0 devices found

Image provided: 'D:\Projects\my-iso.iso'
Scanning image...
ISO analysis:
  Image is an ISO9660 image
Disk image analysis:
  Image does not have a Boot Marker
ISO label: 'MyIsoImage'
  Size: 497 MB (Projected)

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