Hi @rgelb,
There are a few compatibility issues of this application with latest ODBC spec drivers (some details to be found here: Elasticsearch ODBC driver with SQL Linked Server).
The next stack release - 7.7.0, due very soon - should bring backwards support for the most important gaps. I'll update the thread once the release is out.
Note however that the driver and server are, up to this release, in version lock-step; i.e. you'll need a server updated to 7.7.