One of our valued AiSP' reported the following.
We installed SQL Server 2016 on the server, and separately installed SQL Server Management Studio and Backwards Compatibility tools as required. DBUpgrader failed during the install because it couldn't find osql.
We discovered this is because SSMS 18 (released 4/24/2019) no longer includes osql, bcp and sqlcmd. Microsoft is obviously pushing users toward 18 instead of 17. If you don't specifically look for 17.x, you'll install 18.