Two weeks after the release of tvOS 16.3, a small routine update was released this Monday evening: it is tvOS 16.3.1 for the Apple TV and version 16.3.1 of the internal software of the HomePod. Apple says this update brings performance improvements and enhancements, in other words, bug fixes. tvOS 16.3 was an important update: it was the one that brought compatibility with the HomePod 2 and it was the one that activated the temperature and humidity sensor of the HomePod mini.
For installing tvOS 16.3.1 on Apple TV, you can trigger the manual installation of this new version in the Settings app > System > Software Updates > Update Software. To update HomePod, go to your home settings in the Home app on your iPhone or iPad.