The record sorting order is based on the Airtable view selected in the view's configuration. You can find the option by going to:
Tables
Select a table
Select a view in the Views section
Under Filter and Sort, select an appropriate Airtable View to apply its filter and sort settings.
When no Airtable view is set, the view will be marked as "random order" in the views list, since there will be no sorting applied.
Manual sorting options are also available for the portal user, if the appropriate toggle is enabled in the User Actions section.
The Interface also allows you to select which Airtable views you want to display during the creation process.