Soundiiz Export Mode

To start a multi-selection: Either right-click, or long left click, or short left click while holding Ctrl. Add to multiselection by clicking additional ones or hold Shift while clicking another one to select the range between first and last. (You can also select multiple ranges together). To select all, press Ctrl+A right away or start a multiselection and choose All from the menu top left.

The above is on PC and Mac. On mobiles, long tap to start multiselection, then tap more items. There is no range option