Boy, hoping not to have to post this, so lame, sure enough, googled and can't see anything on it.
With itunes. I think was option click top and all checkboxes for songs would de-select. And there as a menu for it too. In With "Music" stumped, can't figure it out. Thanks!

AH, Is in menu a deselct all, but after I click that, all boxes still have checkmarks. When I click a box, then disappears and order jumbles, maddening. Lost.

I don't remember iTunes, but there's apparently no way to UNCHECK all in Music.

The SELECT/DESELECT all options deal with coloring/un-coloring all items blue, NOT with the checkmarks.

The only way to uncheck all appears to be by hand...one at a time, but the order doesn't really jumble. What happens is that the unchecked items move down to the bottom of the list.

I suggest that you submit a feature request here.