Samsung discontinues Galaxy S9 series software support
The Galaxy S10 series meanwhile were moved from monthly to quarterly updates, now that they are over 3 years old.
The Galaxy S9 series is following the path of its predecessors. Back in early 2021, Samsung demoted the S9 from monthly to quarterly security updates, when the Galaxy S8 was completely taken off the list, and the same thing happened to the Galaxy S7 phones a year earlier.
The Galaxy S9 series' last major update was to One UI 2.5 package, received in late 2020.