code: def _populate_bookmarks_list(self):
          
          # Connect to the QGIS sqlite database and check if the table exists.
          # noinspection PyArgumentList
          db_file_path = QgsApplication.qgisUserDatabaseFilePath()
          db = sqlite3.connect(db_file_path)
          cursor = db.cursor()
          cursor.execute(
              'SELECT COUNT(*) '
              'FROM sqlite_master '
              'WHERE type=\'table\' '
              'AND name=\'tbl_bookmarks\';')
  
          number_of_rows = cursor.fetchone()[0]
          if number_of_rows > 0:
              cursor.execute(
                  'SELECT * '
                  'FROM tbl_bookmarks;')
              bookmarks = cursor.fetchall()
  
              canvas_crs = self.canvas.mapSettings().destinationCrs()
  
              for bookmark in bookmarks:
                  name = bookmark[1]
                  srid = bookmark[7]
                  rectangle = QgsRectangle(
                      bookmark[3], bookmark[4], bookmark[5], bookmark[6])
  
                  if srid != canvas_crs.srsid():
                      transform = QgsCoordinateTransform(
                          QgsCoordinateReferenceSystem(srid),
                          canvas_crs,
                          QgsProject.instance()
                      )
                      try:
                          rectangle = transform.transform(rectangle)
                      except QgsCsException:
                          rectangle = QgsRectangle()
  
                  if rectangle.isEmpty():
                      pass
  
                  self.bookmarks_list.addItem(name, rectangle)
          if self.bookmarks_list.currentIndex() >= 0:
              self.create_bookmarks_label.hide()
          else:
              self.create_bookmarks_label.show()
              self.hazard_exposure_bookmark.setDisabled(True)
              self.bookmarks_list.hide()
docs: Read the sqlite database and populate the bookmarks list.
  
          If no bookmarks are found, the bookmarks radio button will be disabled
          and the label will be shown indicating that the user should add
          bookmarks in QGIS first.
  
          Every bookmark are reprojected to mapcanvas crs.