> on Windows I can mindlessly drag cursor to the top-right of the screen and click to close current window. ...

Try that with GOG Galaxy (it's app-dependent).

Great example. I'm talking about the default behaviour of apps in the OS.

GOG Galaxy is an app that redraws everything from scratch with bad UI.

It's funny because they use floating controls with excessive spacing, just like Apple's new theme. And that was the culprit in their case: https://i.imgur.com/dsey4c3.png

I would file a bug if I worked there as QA.