Apple launched iOS 15.5 on May 16. Now it’s stopped signing iOS 15.4.1, which means you can’t downgrade back to that version once you install iOS 15.5.
According to Apple’s release notes, iOS 15.5 has these improvements and bug fixes:
– Wallet now enables Apple Cash customers to send and request money from their Apple Cash card
– Apple Podcasts includes a new setting to limit episodes stored on your iPhone and automatically delete older ones
– Fixes an issue where home automations, triggered by people arriving or leaving, may fail
As noted by macRumors, Apple routinely stops signing older versions of software updates after new releases come out in order to encourage customers to keep their operating systems up to date, “so it is not unusual that iOS 15.4.1 is no longer being signed.”