It's a bit more of a story than just geodatabase version to ArcGIS Server version. There's the whole driver, and database version thing to consider as well.
10.9.1 - https://enterprise.arcgis.com/en/system-requirements/10.9.1/windows/database-requirements-oracle.htm
11.2 - https://enterprise.arcgis.com/en/system-requirements/latest/windows/database-requirements-oracle.htm
Fortunately for you, both support 19c! 🙂
You also need to consider support for drivers, which I don't think will be an issue here.
You also need to consider what versions of ArcGIS Pro you are using and their support to that database version and geodatabase version.
Geodatabase now offer a degree of forward/backward compatibility. It used to be that you kept them at the lowest common denominator. There also used to be a matrix saying exactly what GDB versions were supported by application version. Now the 'advice' is stay as close as you can.
Obviously, if you use a 11.2 GDB with 10.9.1 then 10.9.1 will not be able to use any new functionality in there.
You also need to consider if you're using advanced types, like Parcel Fabrics or Utility Models. In those situations, I believe there are strong rules about Pro versions being matched to Enterprise versions, being matched to EGDB version and possibly even database versions.
Quite a bit to consider, sorry if I've muddied the waters.
Scott Tansley
https://www.linkedin.com/in/scotttansley/
