In Aspose.Diagram 26.1, a ContainerProperties property was added to shapes and are populated if the shape is a Visio container. Also, Page.DropContainer() was added to add a container to a page.
Unfortunately, Containe…...are identical according to the API: $doc = New-Object Aspose.Diagram...in Aspose.Diagram 26.1. You reported that although the ContainerProperties...