Samsung is now rolling second One UI beta update to the Galaxy Note 9 users that fixes several bugs and bring features improvements. It includes the December 2018 security patch.
As the first recipient of the One UI beta test, the update is currently rolling out with build version N960FXXU2ZRL6, while the size of the update is 553.88 MB.
If you have installed the beta build on your Galaxy Note 9, you can check for the update manually by heading into the Settings > Software updates > Download updates manually. This will allow the software to update and load the beta version.