The monthly “Google System Release Notes” primarily detail what’s new in Play services, Play Store, and Play system update across Android phones/tablets, Wear OS, Google/Android TV, Auto, and PC. Some features apply to end users, while others are aimed at developers.
The following first-party apps comprise the “Google System”:
To update, open the Settings app > tap your name at the very top for “Google services” (on Pixel) > All services tab > Privacy & security > System services.
A feature appearing in the changelog does not mean it’s widely available. Some capabilities take months to fully launch.