yes, Oracle 19.3 is the base certified released for the Geodatabase and customers need to apply the Oracle Patches for the reasons I described, hence yes, the Geodatabase is still supported with Oracle 19.16, but read below from the documentation to understand.
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Oracle database requirements for ArcGIS 10.6.x ArcGIS Pro 2.1 and 2.2—System Requirements | Document...
Oracle database patch support
Oracle patches are supported. This includes Oracle patch set levels and Oracle Interim (One-Off) Patch as per Oracle Corporation's Patch Set Overview and Interim Patch documentation.
See Oracle Support for all Oracle patch set (and Interim Patch) documentation and installation instructions. Esri recommends making a full backup of your Oracle database prior to applying any Oracle patch sets or interim patch. If functionality that was working prior to applying the Oracle patch set or interim patch stops working, return to the previous version of Oracle. Contact Oracle support as needed.
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Note: I 've been patching Oracle Databases and Enterprise Geodatabases for over 20 years and on all this time I only run into an issue once and Oracle had to publish an one-off patch to fix the problem.
You shall also update the version of the Oracle Client on the ArcGIS Desktop (ArcMap) & ArcGIS Pro machines and ArcGIS Enterprise servers ( Portal & ArcGIS Server ) to the latest Oracle Client 19.16 (full client) or the latest Oracle Instant Client 19.15.
| Marcelo Marques | Esri Principal Product Engineer | Cloud & Database Administrator | OCP - Oracle Certified Professional | "In 1992, I embarked on my journey with Esri Technology, and since 1997, I have been working with ArcSDE Geodatabases, right from its initial release. Over the past 32 years, my passion for GIS has only grown stronger." | “ I do not fear computers. I fear the lack of them." Isaac Isimov |