Apple has just released the stable version of iOS 15.4 to iPhones of the 6s generation or later. It is viewed as an important update to many, as it is the one that adds mask-compatible Face ID to the flagship mobile devices. However, a certain number of users have taken to social media to complain of severely reduced screen-on time thanks to this latest software version.
https://www.notebookcheck.net/The-iOS-15-4-update-meets-with-reports-of-sudden-onset-battery-drain.609086.0.html