This belongs in Mac Technical Support, as the issue doesn’t pertain per se to in-game matters.
For anyone still experiencing this issue, I found a very reasonable workaround!
In Graphics options, choose the “Fullscreen” Display Mode. Then, when in full screen, press ⌘M on your keyboard to return to a windowed mode. This version of the window can be resized arbitrarily!
It seems this is broken with the “Windowed” mode specifically, though “Fullscreen (Windowed)” is what you want to be able to resize the window.
4 Likes