According to release notes from Apple, iOS 15.3.1 and iPadOS 15.3.1 fix an issue that could case the Braille displays to stop responding. This means that the visually impaired users of the iPhone or iPad will have trouble if the Braille displays stop working. Further, the company notes the important security updates that include fixing a WebKit bug that could allow arbitrary code execution via a malicious web content. Apple says that it is aware that the vulnerability may have been exploited and notes that it is important for iPhone and iPad users to update their devices to iOS 15.3.1 and iPadOS 15.3.1 as soon as possible.

Which devices are getting the update?
The iOS 15.3.1 update is available for iPhone 6S and above, iPad Pro (all models), iPad Air 2 and later, iPad 5th generation and later, iPad mini 4 and later, and iPod touch (7th generation).