I have a Windows application created using QT.
My icon in the top left of the window is extra tight when the window is maximized. Actually, on my screen, the logo is cropped.
Below is a screenshot of the problem. (It shows the top left of the screen when the window is maximised; notice there is no padding between the edge of the screen and the logo.)

That is the behaviour as designed. Here’s what my app looks like, for example:
If you want to add some padding you’ll need to add it to your icon.