Within the Elastic Admin site you can set the Default Product Sort for each of your catalogs. By default all catalogs will show in UI Controlled (Default) this behaves the same as Catalog Oder. Other defaults that can be set are Inventory, Price, Name, and Number Order. This can be especially useful in ATS or ASAP catalogs you want to have product with the most inventory to appear first when the catalog is opened.
To set your default product sort go to your sites Admin page -> Data -> Catalogs -> Edit Catalog (for the catalog you would like to change) and scroll down til you see Default Product Sort. Selecting your sort and saving your catalog will then set this to be the default. This can be set using a catalog import with development work or will persist if manually set.