On Mojave as of May 2022 CCC v 5.whatever wouldn't create a sparse bundle disk image for me when I selected new disk image as destination. The 'action button' was grayed out.
I switched from the non-admin account I've long used with CCC to an admin account and I was able to do it.
I was able to create disk images using Disk Utility from the non-admin account.
I don't have time or energy to debug further, but if you run into this issue try an admin account.
PS. Once upon a time CCC would just create a disk image if the task referenced one but none was found on the target drive. That's no longer an option, if you are setting up a new drive modern tasks will require the disk image to exist. It's hard to get the 'right' image manually, so you really want CCC to create it for you.
Also, by the way, and unrelated to above, you need to use AFP if you're doing network CCC backup to a sparse bundle disk image.