Apart from monthly security patches for Pixels, Google rolls out frequent Google Play system updates for Android devices. They tend to fix bugs or add new features to many core OS components like location services, Emergency alerts, contact/data syncing, etc. The feature is a part of Project Mainline, which first debuted with Android 10. It allows the big G to update some Android components without rolling out a new OS build or requiring carrier approval. Most users remain unaware of new Google Play system builds since they are automatically installed in the background. However, if you are the curious type, the company now has a support page detailing the improvements in each new build.
Google Play system updates are applicable for phones, tablets, Wear OS watches, Android Auto, and other Google-certified Android devices. This is why the changelog in Google's support page (via 9to5Google) mentions improvements across several different devices. While Play system builds have been rolling out for a few years now, the company only lists the changes starting December 2021. The page also highlights the improvements in the monthly Play Store and Play Services updates.
The December 2021 update brought about improvements to "battery life, device connectivity, network usage, privacy, stability, security, and updatability." The January 2022 update contains improvements for the timezone management system and support for new daylight savings time transition changes in several countries. You can check the Google Play system version installed on your Android phone by navigating to Settings > Security > Google Play system update. The option is tucked under Settings > Biometrics and security > Google Play system update on Samsung phones. These updates are usually automatically installed in the background and only require a restart for the changes to take effect.
Like its monthly security bulletin, Google seemingly intends to update the support page every month, so you will know which exact build to blame when something goes wrong.