#1:
You can put whatever description you want between the single quotes. That is the name that will appear in the Grub menu.
#2:
In the 40_custom file, the exec tail -n +3 $0 must be there. That is the command that copies the menu entry you wrote into /boot/grub/grub.cfg when you run sudo update-grub.
Post #20 is not showing 40_custom file, but the section of grub.cfg that is created by sudo update-grub. That does not have the command included.
#2:
Yes it's normal to see two. It's called the UEFI boot menu - it is NOT the grub menu. You must be pressing a certain key during start up to get this UEFI boot menu.
If you keep hands off during start up, this UEFI boot menu will not be shown, and the computer will automatically boot the first entry in the UEFI boot menu, which takes you directly to the Zorin grub menu (your last picture). It appears to be working now and gives you the Manjaro choice.
I'm glad to see you have it working now. What do you think of Manjaro so far?
Yes, I first pressed the ESC key to get into the UEFI Boot Manager. Then I let the machine continue to boot Zorin. Then the grub menu (pictured in my last post) appeared.
However, if I keep hands off during start up, the computer just boots straight into Zorin, without showing the grub menu.
I'm going to mark this issue as solved. Even though this "UEFI-then-Grub" approach is more of a work-around than a full solution, it does get the job done.
Manjaro-wise, I've mostly been focused on this current boot issue, and haven't yet really looked at it.
Meanwhile...
My main goal in exploring Linux is to find or customize a GUI that will work for my visually-impaired wife and others in her situation.
Among other things, this will require fine-grained control of font-size/scaling for individual elements - like: 1) the left-side folders navigator in the File Manager, 2) the file-selection window that opens after pressing Ctrl+O in the browser, etc - without having to scale the GUI globally.
Do you know if this type of fine-grained control is even possible in Linux?
Also, do you think this particular forum would be a good place to get some help on my "Visually Accessible Linux" project? Or maybe there is also some other forum that focuses more tightly on such fine-grained control of the GUI?
Anyway, thanks again for all your help on this boot issue.
I assume you've looked at Settings > Accesibility? I use this to set a larger cursor size that I can see.
You can change the font size in the application windows (which includes the Open file dialog) in Tweaks utility. That should help.
You could ask about these things on other forums - like Ubuntu Forum. Some user there might offer some suggestions.
As to your unusual startup procedure, did you ever try to just change the boot order in the UEFI boot menu so that the capitalized Ubuntu is first on the list?