As expected, they're both relatively minor updates focused on bug fixes and under-the-hood improvements.
After this update, iPhone users will find a new "Network & Wireless" toggle under the Location Services settings under Privacy. The new update fixes the problem with Screen Time and Communication Limits as well as adds the option to disable location tracking by the U1 Ultra Wideband chip in these new-gen phones. iPhone 11 and iPhone 11 Pro users don't need to worry anymore It was revealed in December that the iPhone 11, iPhone 11 Pro, and iPhone 11 Pro Max continue to track users even when location tracking is switched off. A pain when you consider that, for example, in Australia, Ultra Wideband transmitters must not be operated close to selected radio-astronomy sites.
The iOS 13.3.1 update fixes the issue with Communication Limits that allowed users to add a contact without entering the Screen Time passcode.
Apple also included patches for bugs with Deep Fusion editing, FaceTime camera prioritization, and push notifications not showing up over Wi-Fi.
The HomePod OS 13.3.1 update adds support for Indian English voices.
These have now also been fixed with today's iPadOS 13.3.1 release. At that time, it announced that 55% of all iOS devices released in the past four years were running "iOS 13" and 50% of all iOS devices were updated.
There are also some security vulnerability fixes included in the updates, which are typically important reasons to update to the latest software as soon as possible. The iPadOS update lacks some of the cellular and iPhone 11-specific fixes, however.
The iOS 13.3.1 update introduces a toggle to disable the Ultra wideband U1 chip on the iPhone 11 and iPhone 11 Pro series.