Is shift+click or command+click supposed to do something different than regular click? (right now it doesn't)

The documentation says ⌘+click and ⇧+click is to select multiple items. But the same happens with regular clicking (without any keys).

I would say ⇧+click (shift+click) is supposed to select a whole range, for example if you click item number 3 it selects that, and then if you ⇧+click item number 8, it selects all items 3 through 8. And then next if you click item number 14 it will select that (in addition to 3~8 that were already selected). And then ⇧+click number 10, it should select items 10 through 14 (while also keeping 3 thru 8 selected).

Hopefully this description clarifies how it's supposed to work.

Furthermore if you want ⌘+click to have the same behavior as in macOS Finder, then regular clicking an item should only select that item, deselecting any previously selected items. Or if you click an item that was already selected, then deselect it (so it's actually toggle). Whereas ⌘+clicking an item should toggle that item while leaving any other selected items selected.

But the ⇧+click is more important imho.