See following logic: https://github.com/moodle/moodle/blob/7ce003b666a66b465ce9335f430a6e4d3535a7f1/reportbuilder/classes/permission.php#L128-L133

If a user has 'moodle/reportbuilder:editall' capability they can create a report but without 'moodle/reportbuilder:edit' they cannot currently edit their own reports, as per above (although they can edit any reports from other users)