'not' supporting 4k in windows!

You can choose to support 4k resolution or not on a Mac with Unity but what about on windows? I need a windowed app to run half resolution if running in windows at 4k as otherwise it kills the frame rate on lesser laptops (using 2017 LTS)

 

You can choose to support or not support any resolution on any platform (where it does make sense), so what is your question exactly?
https://docs.unity3d.com/ScriptReference/Screen.SetResolution.html

 

That is why I said a 'windowed app' at half resolution - I mean same size on screen as if HD. In any case an end user can choose High DPI Override as System and the app is run half-res interestingly. Otherwise it would take a render texture to force it I guess. If your app window is 1024x768 on an hd screen then you might want it 2048*1536 on 4k but still at internal resolution of 1024x768 double scaled.