“Since Apple took away the ability for 3rd parties (eg, us) to copy the OS, and took on the responsibility themselves, it’s been up to them to ensure this functionality continues to work.”
macOS 15.2 breaks Apple’s own replicator with a Resource Busy error near the end of the copy, and SuperDuper cannot route around it. Apple locked third parties out of copying the OS, then shipped a release that cannot copy it either. The bug is FB16090831. Apple rarely ships updates between now and New Year’s, so bootable backups are dead for the holidays.