When attempting to use the "save as" hotkey (in any software), Greenshot instead opens a capture dialog of either
the image on the clipboard; or
the desktop, if no image is on the clipboard
and does not allow the other application to process the hotkey.
Applications with CTRL+SHIFT+S hotkey bound
I might have misunderstood your issue, if so please try to explain it differently.
But that doesn’t look like Greenshot, we actually don’t respond to CTRL+SHIFT+S unless you specifically configured it like that. The attachment doesn’t show Greenshot either.