If you would like make a bootable copy of your startup disk with CCC 6:
- Choose your startup disk as the source
- Select a destination
- Click on the Destination selector again and choose "Legacy Bootable Backup Assistant"
- Choose the option to create a bootable backup, then run the task
The procedure is documented here:
Creating legacy bootable backups of macOS Big Sur (and later OSes)
But I would like to draw your attention to this section in particular:
Things you should know before relying on an external macOS boot device
In general, we're planning to rely less and less on the bootability of the backup volume for recovery from hardware failure. I explain why in this blog article:
Beyond Bootable Backups: Adapting recovery strategies for an evolving platform
You don't have to be able to boot your Mac from the CCC backup to restore data from it. You can restore individual files and folders using Finder or CCC while booted from your production volume, and you can also recover older versions of files from CCC snapshots. If you ever needed to restore everything from a non-bootable backup, you would install macOS via Recovery mode (e.g. onto a replacement disk), then
migrate data from the CCC backup via Migration Assistant. CCC backups are compatible with Migration Assistant, and we support that configuration.