Disk Utility can’t image APFS volumes, and normally returns an error if you try to image a container. Here’s the workaround.
Use the most recent macOS possible, don’t disable protection, beware of links, if you have to live dangerously, use a VM, and remove Flash now. Practical tips for all.
Do you have VMs or other large files, and use Time Machine for backups? Here’s how to make those backups quicker and more compact.