Prepared patch for grub-x86:
https://pagure.io/fork/mexit/fedora-kiwi-descriptions/c/98fc4a8871afbef32259cdb4ded97d09243ebd59?branch=rawhide

I have no way of testing the other architectures, most likely everything will work when the missing parameter is added.

dracut-ng:
https://github.com/dracut-ng/dracut-ng/blob/2d3d646d016cc7fcb66427ee22a962b980089bb0/modules.d/90dmsquash-live/parse-iso-scan.sh#L5

How to boot directly from ISO:
https://osinside.github.io/kiwi/working_with_images/iso_to_usb_stick_grub2_boot_from_iso.html