Apple has stopped support for updating to iOS 17.6 after releasing iOS 17.6.1.
iOS 17.6.1 was released on August 7, with the Cupertino-based company simultaneously ending support for its predecessor, iOS 17.6. This means iPhone users who have updated to the latest version can no longer go back and downgrade to iOS 17.6.1. Apple usually stops digital signing and allowing downgrades a few weeks after the new version goes live. Those who try will be met with an error message due to a server-side verification check.
The reason why Apple stopped older update digital signing is to keep user devices up to date and therefore, have the latest security patches. As far as content is concerned, iOS 17.6.1 had a bug fix to cover disabling or enabling Advanced Data Protection, while iOS 17.6 had unspecified security updates and bug fixes.