Should User Stories In Product Backlog Always Consist of Product Features And Enhancements?

The guide says that "The Product Backlog lists all features, functions, requirements, enhancements, and fixes that constitute the changes to be made to the product in future releases" The list can be translated to User Stories, but they don't always have to be, correct? The Product Backlog may contain other aspects pertaining to development other than User Stories, is this correct? thank you!

Posted By - Gabriel