As WWDC 2022 is coming, Apple has released their most recent update to iOS which is iOS 15.5. With this rolled out, Apple has disabled the verification for iOS 15.4.1 which means you will not be able to downgrade after upgrading to iOS 15.4.1.
iOS 15.5. brings update on minute details and bug fixes, enables user to limit storage on podcast app and delete old programme to reduce wasted space. Pay Cash from Apple Wallet also added a Request and Send button for easier cash flow management. Home app is also improved and able to prompt user to disable alarm permission.