Working in SDDM 19.4 I have a relational model with 45 tables and 6 subviews. I want to create an sddm model of only the 10 tables in one of the subviews. I use the menu path File.Export.Data Model Design, and select the subview I wish to export. The export that is produced contains the entire 45 tables and 6 subviews. The source model has been constructed over time by importing a number of submodels, and various imports. I have other models that can export subviews only so this appears to be a model specific problem.
I cannot comment since this is a problem for specific case. I can look at the problem if you send me that design.