How to clone startup disk? In the process of upgrading to a new SSD in my iMac 2017 Catalina. After setting everything up using Disk Utility, it is asking if I want to restore from “iMacintosh HD” or “Macintosh HD - Data”  I read here of someone having a similar question but his situation was slightly different. I simply want to clone my existing startup disk so I can swap out the old drive with the new one. Can anyone guide me through this?
Many thanks in advance.
-JJ
Cloning isn’t easy in my experience since you need to first learn a bit about specifics and how to select a proper clone tool tool and understand any filesystem differences between your exact versions of OS.
Why not install a fresh OS on the SSD and then when it first starts migrate everything from the old OS?
Apple tools handle this for you including all the version difference if you choose a different OS on the new disk. And with two disks, you can thoroughly test the new drive before you install it or wipe the internal drive.