Can I make a window be made of glass?

Yes, you can make a window be made of glass using Apple's new design system. The concept of "Liquid Glass" is introduced in several sessions at WWDC, which allows you to create a glass-like appearance for UI elements in your app.

For example, in the session Build an AppKit app with the new design, it is explained how the new design system transforms the appearance of a Mac window by altering the window shape and framing its key structural regions in glass. This includes using the Liquid Glass material to enhance the sense of hierarchy within the window, such as placing toolbar elements on a glass material to make them appear to float above the content.

Additionally, in the session Meet Liquid Glass, it is discussed how Liquid Glass can be used to create a unified design language across platforms, providing a distinct functional layer for controls and navigation that floats above the content.

These sessions provide guidance on how to implement glass effects in your app, ensuring that the glass elements maintain clarity and focus within the UI hierarchy.