My user is seeing "There are no recent End-Users available for this DocGen Package" when clicking the "Select Records" button on the DocGen Package.

This is not an error message but more of a validation message. The testing interface will only display records that has been recently viewed by the user. If the user has not viewed any record from the object that the DocGen Package runs from, then they will see this message.

The user can search for a record by searching a record name or navigate to the record they want to test upon. When they click the button again, they should now see the record available for run.