Within the Elastic Suite Admin site you can set classifications for catalogs to better sort the Catalog Select Screen. These will sort all of your Prebooks and ATS catalogs together and give them a classification header.
To set this up you can label your catalogs from the admin site by going to Data -> Catalogs -> Edit Catalog (of the catalog you want to classify). Scrolling down you will see an option labeled Classification. There are three options you can set your catalog as blank (will sort with no header), ATS, and Prebook. It will then sort these catalogs by the label and then their catalog sort value. This can be added to imports with some development work or if not provided in your import manually changing this value will persist once set.