A Samsung Community forum moderator has stated that the company is reportedly working on delivering the One UI update to Samsung Galaxy S9 and Galaxy Note 9 users. Unfortunately, there is no word about when the firmware will be available for download, but it is reassuring to know that it will make its way to the devices eventually.
https://www.notebookcheck.net/One-UI-2-1-update-for-Samsung-Galaxy-S9-and-Galaxy-Note-9-reportedly-under-development.462615.0.html