Apple has ceased signing iOS 15.3.1, which means that the iPhone will no longer be able to downgrade to it. As a result, anybody looking to upgrade to the latest version of iOS will have to do it through iOS 15.4.
To ensure that iPhone owners get the most recent version of Apple’s software, Apple has been known to cease signing older versions of iOS when fresh ones are released. In addition to new features and bug fixes, newer versions of each programme also provide performance and security upgrades.
Apple has officially blocked downgrades to iOS 15.3.1, so anybody who seeks to restore an iPhone will now only have iOS 15.4. Those on the developer and public beta trains may, of course, continue to install the most recent versions of iOS after the official release date has passed.
In spite of this, it’s very uncommon for those who have troubles with a newer version of iOS to be able to downgrade to an older one as a safety net. Until Apple publishes an updated version of iOS 15.4, those who are having problems should stick with iOS 15.4.
In addition to the ability to unlock your iPhone using a mask, iOS 15.4 is the most recent public release of iOS 15.