Can't add to a selection by pressing shift mac

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Hi, I am in GIMP 3.0.2 on mac book, works perfectly, I need to add to a selection, the search says To add to a selection in GIMP, hold down the Shift key while making a new selection with any of the selection tools, and the new selection will be added to the existing one.
I hold Shift and nothing happens, I think these searches are not made for mac. Thank you