For the brief time I used Windows 11 the amount of times I placed a window over another and then clicked on the wrong window because I couldn't tell at first glance where one started and the other ended was absolutely ridiculous.

I'm afraid that the core of the problem is something far more simple and fundamental.

The people designing desktop apps today simply never learned the conventions that make desktop applications good. They grew up with smartphone apps, web apps, electron apps, games, etc.

In fact, you can observe from things like JavaFX, Flutter, WPF, etc., that the trend has long been about the ability of easily creating custom widgets like you could with Javascript (or Flash), rather than the convenience of having a library of widgets that look and feel exactly the same as every other widget in the system.