This update is currently rolling out in India and expected to be available soon in more regions. The original timeline for these devices was January 2020, but it is available earlier than the given timeline.
The software version of this update is M205FDDU3CSL4 and M305FDDU3CSL4 for the Galaxy M20 and Galaxy M30 respectively.
About the changelog, it comes with all the Android 10 features along with Samsung’s One UI 2.0 experience. It also brings the December 2019 security patch.
If you have any of these two devices, you can check for the update manually by heading into the device Settings and go to Software Update, and then tap on the Download and install option.