Kerberos broken on 21H2, domain authentication fails

The Windows 11 21H2 version of November’s Patch Tuesday carried the same Kerberos authentication catastrophe as its 22H2 sibling KB5019980. Domain sign-ins failed. Direct Access connections broke. ODBC database connections stopped working. Microsoft had managed to break the same critical authentication infrastructure across multiple Windows versions simultaneously, ensuring that no enterprise was safe regardless of which supported version they ran. The emergency patch took nine days.