SQL Native Client supports SQL Server only up to version 2012. Afterwards the Microsoft ODBC Driver 17 for SQL Server should be used (> SQL Server 2016).
In regards to that the Automic documentation is outdated:
Release : 12.3.9
Component : AUTOMATION ENGINE
The issue has been confirmed to be a bug and will be fixed with an update of the documentation for V12.3 and V21.0.