I've been running my tests on an IRIS docker image. I have now switched to a Windows VM, just to see if this works better (IRIS for Windows (x86-64) 2024.2 (Build 247U) Tue Jul 16 2024 09:57:03 EDT).
I have also extended my attempts. Like the first time, I used a gateway connection to an IRIS 2024.2 instance (on a docker image), the second GATEWAY connection goes to an MS SQL Server 2022. 

Unfortunately, the THROUGH command still does not work for me. However, the 'old' CREATE FOREIGN TABLE works through the previously created FOREIGN SERVER. This indicates that the configuration of the FOREIGN SERVER and its connection is correct.

1. THROUGH to a IRIS 2024.2 Server works not
2. CREATE FOREIGN TABLE to a IRIS 2024.2Server works  
3. THROUGH to a MS SQL Server 2022 Server works not
4. CREATE FOREIGN TABLE to a MS SQL Server 2022 Server works

But now the error is a different one ;-)

I have no idea how the THROUGH command works...

SQL DATA LENS is now available from the Microsoft Store for easy installation: check it out here

I've tried it on Windows 11. With your information I've searched again and found (my) problem now! First: Thanks for that! 

What was the problem?  
I've installed IRIS using the custom option and selected to install ALL items on the hard disk. Then I cannot find the odbc driver dll in the following folder:

All the other drivers are there: dotnet, java and so on.

Now I've tried a client installation on a fresh Windows... the folders are still empty. BUT the ODBC Data Source Administrator shows the 2024.1 IRIS ODBC driver! 
Again: The CLIENT install works!

The files are located here:


The puzzle is solved. Thanks to all of you!

Andreas