i'm try to perform multiple selection of requirements by means of Ctrl and/or Shift keys. But it does not work.
Is there a specific way to perform multiple selection in PTC Integrity Modeler?
You can't do it in the browser pane up top, but you can multi-select in the content pane.
As mentioned above, multi-select is possible on diagrams. Either use Shift, Ctrl or drag an area on the canvas