Apple Releases iOS/iPadOS 15.4.1 With iPhone Battery Drain Fix
You can download the minor update by going to Settings > General > Software Update on your iPhone or iPad.
Here are the release notes from Apple:
This update includes the following bug fixes for your iPhone:
Battery may drain more quickly than expected after updating to iOS 15.4
Braille devices may become unresponsive while navigating text or displaying an alert
Made for iPhone hearing devices may lose connection within some third-party apps
The bug fix update comes a little more than two weeks after the arrival of iOS/iPadOS 15.4. That major update brought a number of new features including Face ID with a mask and Universal Control on the iPad and Mac.