The recent versions of Ubuntu and XUbuntu 24.04 ISO files do not contain a \boot\grub\i386-pc\core.img file but instead contain an eltorito.img file. Older versions used syslinux.
I am not asking about booting from an ISO file, but about booting from the files extracted from the ISO using grub4dos to run grub2 and load the grub2 menu system.
Previously I could use the kernel command in grub4dos to load the core.img file but this does not work with eltorito.img and I get a grub rescue prompt instead.
Perhaps because it is looking for a CD/DVD device?
Is there a way to copy the Ubuntu ISO file contents onto a FAT32 USB drive and then legacy boot those files from grub4dos?
I know we can use kernel and initrd, but this requires a bespoke menu to be created for each different ISO.
I infer that Rufus seems to need to download syslinux and add that to an Ubuntu ISO in order to make it legacy bootable...?