You can still write code that targets Windows XP and it will run on Windows 11 just fine. There's no compatibility break. The problem is that newer versions of

You can still write code that targets Windows XP and it will run on Windows 11 just fine. There's no compatibility break. The problem is that newer versions of Windows offer plenty of features which make library implementation simpler and/or give better performance. Someone else mentioned some threading/synchronization APIs, which is also the most common non-XP feature I've found in use in various C++ libraries.