Suppose you instantiate a window w/ SDL_CreateWindow, then because of the time required to build your window content, is it possible that by the time your UI is constructed, the “automatically awarded” focus usually given to a newly created window will have timed out? The symptom would be a window that does not have focus and will not gain focus by clicking on the window (or title bar for desktops). The window will regain focus by being minimized and restored or by setting the focus elsewhere and restoring the new window to the top of the window “stack”.