/sbin/init in rootfs not found

[fredmyra]

I am trying to add Mocaccino OS's iso to the multiboot hybrid usb, with isos of several Linux distros, which I travel with.

I am testing on a Bios machine(Fujitsu Lifebook) and I am getting the error:
/sbin/init in rootfs not found.

The struture of the usb is the following:

sdc      8:32   1  57.8G  0 disk 
├─sdc1   8:33   1    33M  0 part # bios boot
├─sdc2   8:34   1   512M  0 part # ESP
├─sdc3   8:35   1     8G  0 part /run/media/anon/artix
└─sdc4   8:36   1  49.2G  0 part /run/media/anon/ISOs

Where sdc3 contains a minimal, base install of artix Linux which holds Grub.

Path to Moccacino's iso is:
/ISOs/MocaccinoOS-MATE-0.20220903.iso

I have also expanded its content to: /ISOs/loop_mountingMocaccino

I have been trying different menu entries by varying which version (iso vs expanded) and which value I assign to root in the linux command line.

My grub.cfg (I adjust linux line for different linux line options,under booting

# Config for GNU GRand Unified Bootloader (GRUB)# added sysrescue 5.2.2 dec 18 2022
# /boot/grub/grub.cfg
# januari 12, 2023
# Timeout for menu
  set timeout=-1
# Default boot entry
  set default=0
# Menu Colours
  set menu_color_normal=white/black
  set menu_color_highlight=white/green
# persistent block device  naming
# define globally (i.e outside any menuentry)
  insmod search_fs_uuid
  insmod gzio
  insmod part_gpt
  insmod part_msdos
  insmod fat
  insmod loopback
  insmod iso9660
  insmod ext2
  insmod all_video
  set gfxpayload=keep
  set root=(hd0,gpt4)
menuentry "MocaccinoOS.iso" {
   linux /loop_mounting/Mocaccino/boot/kernel.xz cdroot rootdelay =7 nomodeset failsafe # vga=ask 
#  linux /loop_mounting/Mocaccino/boot/kernel.xz root=LABEL=ISOs rootdelay =7 nomodeset failsafe # vga=ask 
  initrd (loop)/boot/rootfs.xz
}
menuentry "MocaccinoOS iso expanded" {
  set isofile="/MocaccinoOS-MATE-0.20220903.iso"
  loopback loop (hd0,gpt4)$isofile
  linux (loop)/boot/kernel.xz cdroot rootdelay =7 nomodeset failsafe # vga=ask 
  initrd (loop)/boot/rootfs.xz
}

option iso with cdroot gives the no /sbin/init error in the context of "no proper overlay structure" as in screenshot 'overlay_case':

option 'iso with root=LABEL=ISOs' gives the no /sbin/init error in the context of "/loader: line 43: =7: command not found" as in screenshot 'loader_case'

option 'expanded with cdroot' same as with 'iso with cd root'

option 'expand. w root=LABEL=ISOs' same as with 'iso with root=LABEL=ISOs'

I have the 'MocaccinoOS-XFCE-0.20221226.iso.tar.xz' but since I had started the tests with the older version, which boots swiftly when dd-ed to an usb drive, I did not want to introduce an additional variable.

I will be thankful if anyone can provide any guidance.