Hello,
That is a Standard Menu designed for multiple screens. based on the Screen options, SAP was enabling and disabling the functionality. Usually, these funcations will be enabled by SAP when you have check box in your list. LT23 is report will not have check box. That is the reason, It is disabled. If you check LS06/LS11 will have check box. In those kind of screen, these select all/deselect all option will be enabled.
I mean to say, If you have check boxes in your report, then these buttons will be enabled and it makes sense.
let me know, If you need any more information.