If that does not produce a bootable volume, and if you have exhausted the Firmware Discoverability Troubleshooting steps below, then we recommend that you install macOS onto the backup. When you make a backup of a Big Sur startup disk with CCC 5.1.23 or later, CCC will automatically use Apple's proprietary APFS replication utility (ASR) to make an exact copy of the source. This volume is cryptographically sealed, and that seal can only be applied by Apple ordinary copies of the System volume are non-bootable without Apple's seal. Starting in macOS Big Sur, the system now resides on a "Signed System Volume". MacOS 11, "Big Sur" bootability troubleshooting
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