iOS 15, iPadOS 15, and macOS 11 add strong cryptographic protections to system content with a signed system volume (SSV).
support.apple.com
Note that if the APFS Copy Utility (CCC Legacy Bootable Backup Asst) gets any I/O error, such as media error which I have seen from an seemingly otherwise working Samsung 980 Pro NVMe SSD, the clone operation fails with a cryptic error msg and the target is not usable. The "signing" part of SSV can not tolerate I/O errors, period, which is a good thing, but the poor error reporting may leave feeling that Apple is working against you.
Basically since Monterey, the core OS is verified to be intact and not tampered with or disturbed by errors as supplied by Apple, which like soldered RAM / drives is increasing system reliability. But to old PC nerds, it feels aggravating, like losing options.
You can use CCC Data partition cloner to incrementally backup your account, but if any update is applied since the original bootable backup was made, the target is likely to no longer be bootable, and requires the target to be erased to make another full bootable clone. For this reason, CCC recommends just making Data partition clone and recovering by doing a clean-install of macOS then bringing your user data in via Migration Assistent.
For those with need to recover at short notice, one way to preserve the old style bootable backup is to only update macOS manually on a schedule the corresponds with your willingness to make a full clone, say once or twice a year, so you can keep doing incremental updates of user data to the backup.
If you are using a true Mac overall reliability should be getting high enough that only Data backups make sense because the the most historically failure-prone parts are now solid-state, vetted, and tamper proof.
Like the iPhone, no one's dies any more, it gets lost or broken; the idea of a phone drive or RAM failure extremely unlikely.
CAVEAT: Think through your backup plan according to your risks / needs.
But basically this SSV change is a good thing,