Is it posable to create a disk image

I have OCLP installed on a 2012 Mac mini. I use this machine for experimenting, and learning. Often I load software or mis configure thing and break the system, and that is what it is there for. I would like to have a base setup with some programs and then create a disk image. I usually use Carbon Copy Cloner on my main Mac (non OCLP), With my2012 mini I copied the system drive to an external USB SSD but could not get the external drive to boot. I then tried to read an image with clonezilla and ran into the same problem. I guessing it may have something to do with the efi partition. What should I try next.