How does pi64-desktop join the berryboot startup item list?

[lavenus]

After downloading pi64-desktop.zip, unzip it to get the pi64-desktop.img size of 2.88GB. Run the following command on the X86-64 computer according to the berryboot official website.

$ sudo kpartx -av pi64-desktop.img
Add map loop0p1 (252:5): 0 117187 linear /dev/loop0 1
Add map loop0p2 (252:6): 0 3493888 linear /dev/loop0 118784
$ sudo mount /dev/mapper/loop0p2 /mnt
$ sudo sed -i 's/^\/dev\/mmcblk/#\0/g' /mnt/etc/fstab
$ sudo sed -i 's/^PARTUUID/#\0/g' /mnt/etc/fstab
$ sudo rm -f /mnt/etc/console-setup/cached_UTF-8_del.kmap.gz
$ sudo rm -f /mnt/etc/systemd/system/multi-user.target.wants/apply_noobs_os_config.service
$ sudo rm -f /mnt/etc/systemd/system/multi-user.target.wants/raspberrypi-net-mods.service
$ sudo rm -f /mnt/etc/rc3.d/S01resize2fs_once
$ sudo mksquashfs /mnt new-pi64-desktop.img -comp lzo -e lib/modules
$ sudo umount /mnt
$ sudo kpartx -d pi64-desktop.img

Finally get newpi64-desktop.img with a size of 885MB, but the last boot was unsuccessful and the kernel init failed to load. How to import to berryboot as part of the startup item?
The following is a reproduction of the problem