Expanding Lookup and filtering based on a value in related Entity - Web API roadblock

If you're looking to expand lookup and filtering based on a value in a related entity, this tutorial might be helpful. However, the author encountered a roadblock while achieving this through Web API, and had to use fetchxml to get the expected output. The author posted about this issue on Stack Overflow and raised a Github issue. Microsoft provided active support for their queries and confirmed it as expected behavior. In summary, the scenario involves getting all the Entity A records with an expected attribute value (filter) in related Entity B lookup, and it should work in a way like INNER JOIN, to filter out Entity A records with blank lookup. However, the result turns out to be LEFT OUTER JOIN, and even blank records without filter attribute value are returned. The post provides the Web API Query and both the expected and actual output. But they note that Web API endpoint cannot help in this case and instead you should use fetchxml for getting this expected output.