The iOS 11.3.1 is not a major update by any means and it has been rolled out only to fix the display issue that some iPhone 8 users were having after updating to iOS 11.3 that was rolled out last month.
Apple addresses the issue in its latest update, claiming that "iOS 11.3.1 improves the security of your iPhone and iPad and addresses an issue where touch input was responsive on some iPhone 8 devices because they were serviced with non-genuine replacement displays".
In comparison, the majority of Android installs (26%) are on Marshmallow, which first debuted back in 2015, followed by Nougat at 23%, which debuted in 2016. Various third-party screen suppliers also stated that the issue prevented customers from opting for cheaper means to fix their faulty iPhone units than an authorised source.
Prior to today, Apple iPhone X users who wanted to use the Amazon Alexa app had to deal with ugly black bars at the top and bottom of the screen. From Settings, tap the General tab and Software Update respectively to unlock the update.
The iOS 11.3.1 update is nowhere as major a software build as the iOS 11.3 package that was created to enhance the user experience by letting users toggle performance throttling and view battery health. Also, it is recommended to take a backup of all the files before proceeding with the update.
Reports two weeks ago noted that two different issues had appeared when iOS 11.3 discovered that replacement screens were installed in recent iPhones.
Further notes on the security content of the update reveal fixes related to memory corruption issues and spoofing issue in the handling of URLs. Then the buyer makes the "right" choice and goes to the App Store.