Unfortunately, this issue has nothing to do with the CData ODBC driver itself, as our tool supports UPSERTS wherever applicable. The problem here is that SQL Server Management Studio itself does not support upsert operations, hence why the query editor does not recognize it as a valid function.
While our documentation does cover supported SQL methods such as upsert and getdeleted (which can be accessed and used from any tool that supports it), SQL Server Management Studio does not so you will be unable to use specific methods like this from this particular tool. Instead, you'll need to manually create a script that achieves the same function.
For example, you can replicate the UPSERT function in SQL Server using the supported MERGE command: https://www.hackdeploy.com/how-to-run-a-sql-server-upsert-using-merge/