This is an extract taken from Samsung Members - Korean Community. Answering to the question of a user, this was what he said. Although there is no timeline on when will this update will be released but here is what he said.
The One UI 2.1 update is a new application, including the camera applied to the latest products such as the S20. It is not applied because it is judged that it is difficult to guarantee optimal performance in the Note 9 situation. However, we are doing our best to listen to customer’s voices more and make better products, and we are currently checking and applying the features that can be added with One UI 2.1. Please note that the response is late due to a careful review process to provide a positive response. We will do our best to prepare and provide stable software. Thank You.
If this is true, then we can see the most waiting software version on the Galaxy Note 9 in the coming weeks or months. The response is only for Galaxy Note 9, so there is no word about the release for Galaxy S9/S9+. We have to wait for a while to hear about the release for Galaxy S9 from the official team.