Since Oracle 18c after you successfully apply the patches on the database binaries you will notice that when you invoke sqlplus after that…the version is immediately changed/reflected:

In 19c, after patching the database binaries sqlplus is referencing 19.4 version number

This is due to changes being reflected in a file called “oraversion” under $ORACLE_HOME/bin directory

For example:

$ORACLE_HOME/bin/oraversion -baseVersion

$ORACLE_HOME/bin/oraversion -compositeVersion