Failed USB boot

This post is intended to provide (helpful?) information. The post is
the result of a frustrating failure with trisquel_10.0.1. The key
point is that Trisquel will not do what LinuxMint and PureOS will do.

I bought a new laptop to replace one that is dying; the new machine
is a Lenovo Ideapad Slim 9i. I have been unable to install Trisquel
on this Lenovo. However, I have installed LinuxMint successfully. My
preference is Trisquel; but you get what you get 8-)

Using dd, I created boot USB drives for trisquel_10.0.1_amd64.iso,
pureos-10~devel-gnome-live-20220602_amd64.iso, and
linuxmint-20.3-cinnamon-64bit-edge.iso. LinuxMint and PureOS each
booted successfully from their respective USB on the dying laptop,
the new laptop, and another desktop Lenovo. Trisquel booted
successfully on the old laptop, and the desktop, but produces a blank
screen on the new laptop. I tried more than once. At some point I
successfully installed LinuxMint onto the new laptop hard disc.

I tried to boot directly from the Trisquel .iso copied to the
Linuxmint installation on the new laptop; see
https://www.howtogeek.com/196933/how-to-boot-linux-iso-images-directly-from-your-hard-drive/
But I gave up after three attempts since I was unable to get the grub
installation correct, and I do not have enough knowledge of what is
going on to make it worthwhile to pursue further. However, if anyone
can tell me the correct incantation for 40_custom I am willing to try
it.

#!/bin/sh
exec tail -n +3 $0
# This file provides an easy way to add custom menu entries. Simply type the
# menu entries you want to add after this comment. Be careful not to change
# the 'exec tail' line above.

menuentry “trisquel_10.0.1” {
set isofile=”/home/dajo/Test/OS-iso-etc/trisquel_10.0.1_amd64.iso”
loopback loop (hd0,3)$isofile
linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=${isofile} quiet splash
initrd (loop)/casper/initrd
}