What the documentation is conveying: We have certified that version of Oracle (19.3.0.0) in our testing. Then when new patch sets are released (like 19.4, .5, .6, etc.) it would fall under https://support.esri.com/en-us/technical-paper/supported-environment-policy-3521
Non-certification of an environment does not necessarily mean it is not supported. That environment is supported if it meets or exceeds the base build environment and that environment is known to not fail. Environments that are known to not work are usually documented on the product support page as soon as that information is available.
An environment may be supported even if there are some known issues with the software on that particular environment. Any known issues will be documented in the "limitations" section of the System Requirements for that environment.
Support of an environment means Esri will do everything reasonably possible to support and correct problems. Some problems are not solvable by Esri (for example, RDBMS bugs, operating system bugs, Web server bugs, or compiler incompatibilities). Sometimes Esri's support of a site will require the site to upgrade the environment. If no other reasonable alternative is available, and Esri cannot fix the problem, we may provide a patch. Patches will be provided using our existing methods for building and releasing patched software.
Esri cannot support any environment not supported by the vendors of the operating systems, RDBMSs, or Web servers.
--- George T.