Findwindowa Not Finding Some Windows

FindWindow only finds top level windows. If you are searching for an exact match with the title of the window, then you must take into account hidden characters (space, tab, etc.).

Even if you find the window title, it will only work if that window isn't localized—i.e., if the program that creates that window is localized for a different language, then you must also localize your search string.

A more reliable approach is to search for the class name, since this will typically not be localized: FindWindow("myclass", NULL);

Of course this will still fail if there is a hidden top level window that creates a child window containing the window you are looking for. To get that window, you can call EnumWindows to get the handle of each top level window, and for each top level window found, you then call EnumChildWindows.

Fortnite's window has a space or two

sd.Flags = DXGI_SWAP_CHAIN_FLAG_ALLOW_MODE_SWITCH;
sd.OutputWindow = FindWindow((L"UnrealWindow"), (L"Fortnite  "));
sd.SampleDesc.Count = 1;
sd.Windowed = TRUE;