Update: The update is now available for non-beta Galaxy Note 9 users in Germany. The size is 1592.26 MB.
The stable One UI update is rolling out with software version N960FXXU2CSA2 and comes with the January 2019 security patch. The size of the update is 130.77 MB.
If you want to check for the update manually, you can head into the Settings > Software update.