QT is one of the solutions for porting cocoa to windows, but even qt is limited... in a good way. i mean youre not gonna want to program a windows application with ios features in mind like screen shaking.
other solutions consist of devolpers porting cocoa functions and they as well as qt can be incomplete even within the realm of possibility like volume buttons and clicking to change views, etc.
this is the essence of toolchains and frameworks
research those as they are available on swift for windows etc
there are several ways that porting code is possible.
binary, compiler infrastructure are the things that come to mind
sorry if this answer seems uninformative, counter-methodical/"rebellious" or philosophical
Edit: cocoapods.org
Edit: https://swift.org/blog/swift-on-windows/
Edit: http://www.wxswift.org/
there are currently no libraries for writing swift apps on windows, and cocoa is currently only working on ios macos etc
Edit: I recently learned that you can port over existing code onto other platforms via simulation systems like sandboxes and the Wine application on mac which allows 32 bit windows apps to work on mac. if you want to make an app for everyone, then youll have to bundle it with one of those structures - as simple as possible
hope you find this useful
im a beginner swift programmer so this is new to me too