Hi,
We are sorry that this is impacting you.
We are planning on fixing the issue that you mention with the 1.23 release of Anbox Cloud. Please see the release roadmap for more information.
In the meantime, you can continue using the AMS SDK v1.20.2.
For your use case, you can first create an AMS application, and use that to create a new streaming section by using the Stream Gateway API.
The discussion at Request for Documentation and Guidance on POST /1.0/sessions Endpoint in Anbox Streaming Gateway might be of interest to you.