This is what the resize box is/was for. (It's actually draggable edges with no "meat" to them, which introduce the conflict by overloading an element, which is also just a pixel wide.)
*) The resize box used to sit below the very bottom of the vertical scrollbar, just below the down arrow button, as a distinct and dedicated handle for resizing windows. Mind how this is in the direct vicinity of any scroll buttons which may be used to see more than what is exposed by the initial view. It's the quasi "natural" origin and anchor of any basic interactions with the viewport. (Somewhat ironically, while the resize box has mostly vanished from application UIs, it is still rendered by web browsers in certain circumstances. E.g., with textarea elements with scrollbars and resize enabled. With most UIs, there will be no related scroll buttons anymore, though.)