Yes, a headline as funny as it is dangerous, in case you need a bootable backup.
Maybe your job is extremely time-sensitive and you always need to have a backup that is bootable. The advantage of this is that if your Mac’s internal storage breaks, you just connect your external SSD with the backup on it, boot up, and continue working as if nothing happened. You can then repair, reinstall, or restore a backup over the weekend.
Mike Bombich the developer of the Carbon Copy Cloner, which we have listed here in our overview (please make a backup if you don’t have a solution yet) now writes, that a backup of macOS Catalina 10.15.5 is no longer bootable, because Apple has introduced either a bug or a new feature (for those who are technically interested: chflags() can no longer set the SF_FIRMLINK flag on an APFS volume).
In short: newly created bootable backups are no longer bootable, although no error is displayed during creation! Of course, this becomes critical at the moment of backup deployment. Therefore you are now warned. It’s not bad for already created backups under 10.15.4 which were updated later, the problem only occurs when a bootable backup is created under 10.15.5.
As long as Apple doesn’t say anything about the situation, you can use a Carbon Copy Cloner version in beta status, which circumvents the problem for now.