Integrating Deployment Slot Hosted App Service to API Management
In Azure, there are deployment slots within API App service as we have created it for Test, Stage, Preproduction, and Production. But in APIM, we couldn't select a specific deployment slot through hosted app service to Add APIs. Finally, we used Open API Specification.

Thank you for the feedback! We added this suggestion to the backlog and will update the item when we prioritize it for implementation.