I'm a new refugee from W11, so please bear with me - I'm learning as I go, but this question stumps me, since the existence of the Disks "image" option seems to me to be pointless.
I've successfully taken a number of imagecopies of Zorin, and restored, using the amazing Rescuezilla, so I'm not a complete novice. I stumbled across Disks, which has a "create image" option, but when I try to take an image I get "Error unmounting filesystem". Say what? I'm getting used to the vagaries of Linux, but to offer what appears to be a straightforward imaging app which then throws up meaningless barriers seems to be really a bit pointless. An earlier question on the same problem (now closed) appears to have been resolved by the asker using a Zorin live session to take the image, which to my eyes offers no additional value at all.
Don't get me wrong - Zorin is incredible, and has made my 50th Linux attempt so successful that I have no intention of ever going back to Spy Central, but it's not entirely plain sailing by any means.
Any advice on my misunderstanding of Disks/image would be appreciated. Thank you.
I expect the issue you found is probably due to trying to image the same drive that is mounted and running your ZorinOS:
If you need to make an image of the primary drive on the system (such as /dev/sda), you will have to run this process from a live instance of Linux.
e.g. Run (Gnome) Disks from ZorinOS Live USB.
See this: https://www.techrepublic.com/article/how-to-create-disk-images-using-gnome-disk/
I think most users would tend to use Rescuezilla for disk imaging.
Thanks, zabadabadoo. That makes sense from my years of Macrium and now Rescuezilla experiences. It just appears strange to dangle the carrot of an easy image solution only to find that it's not easy at all. No matter, I can live with it, and it doesn't in any way dent my enthusiasm for Zorin... 
It might help to think of Disks not as an imaging tool, but as a disk management tool, with which you could image. To use a kitchen analogy, deep frying is easier in a deep fryer than a stock pot, but you can absolutely do it in the latter--it's just a general purpose tool, and you're going to have to bring expertise to bear to make it happen properly. That's not to say Disks couldn't be better of course.