Earlier, it was available for the Galaxy Note 9 One UI 2.0 beta users in India but now it is available for non-beta/Android 9 Pie users. It will soon be available to other regions.
The software version of this update is N960FXXU4DSLB and the size of this update is 1900MB. It comes with the December security patch.
If you want to check for the update manually, you can head into the device Settings then tap on the Software update menu and go for the Download and install option.