As far as we know, the User Stories are the way a requirement is defined in bounded context with acceptance criteria. On the other hand, the Product Backlog enlists all requirements, i.e., new feature, enhancements, and existing production issues.
This is not clear, if or if not, the Product Backlog just consists out of User Stories. So, the question here is as follows.
Does the Product Backlog just consists out of User Stories in Agile Development?