https://paste.ubuntu.com/p/2yZh4SzCKW/
i'm a new user, deeply interested in keeping on using my "old" macbook air (2011) with zorin os 15.3. however, every effort to install the os is facing crash when grub installation starts. am asking for support, thanks in advance
I would recommend using newer Zorin 16.x versions if possible 
thanks for your prompt reply. however, i've already tried newer version before, same result...
Did you use rEFInd to install Zorin OS?
https://www.rodsbooks.com/refind/
This is a helpful method for Macbooks.
thanks a lot, i'll try and report
having said i am not a linux expert at all, i've installed refind on a usb flash drive. however, i'm not able to make use of the efi shell as the system blocks with no chance to insert any load option...
moreover, i've just tried to re-install zorin os ex novo, after partition's deletion. installation of grub2 aborts with the error "grub-efi-amd64-signed unsuccesful" on /target/
Maybe I am misunderstanding you, but why install rEFInd on the USB?
https://www.rodsbooks.com/refind/installing.html
It must install to the Computer you are installing Zorin OS on.
This is an EFI boot loader error - Which rEFInd should help with. Alternatively, you could install Zorin as Legacy Boot (MBR, rather than EFI), to work around this issue.
what do you intend with "legacy boot (mbr rather than efi)"? how to try this? again, thanks for your "on line" support
MBR is Master Boot Record.
EFI is Extensible Firmware Interface which was developed to replace MBR.
You can set your computer to :Legacy: which is MBR in your BIOS Settings, usually by tapping an F2 or F8 or F10 key at the motherboard splash screen. Which key depends on the manufacturer.
it seems to me that you're referring to windows keys... if so, i'm trying to install zorin on a macbook air (2011)
Ah good point... I have never used a Macbook...
2011 should be fine; as after 2015, Apple quietly dropped support for MBR boot.
The Option Key? Scroll to the bottom:
sardu pro... it seems to me coming from sardinia island... i'm italian 
I must go away now, so will not be available for "on line" support (not that I have been very much help so far), but exploring how Mac handles the EFI boot loader, compared to Linux, should be the direction to look into.
many thanks again!