Regression in Qt 6.8.0 Beta 2 - macOS window flag (NSWindowStyleMaskFullSizeContentView) doesn't work

Hello,

I attached here the minimal code to reproduce this bug. In the latest stable Qt 6.7.2, setting the window flag NSWindowStyleMaskFullSizeContentView on macOS causes the "contentView consumes the full size of the window" (from here), but in Qt 6.8.0 Beta 2, this stops working, causing the inability to properly create native frameless windows on macOS. This is a major issue that I know will affect many users.

Here's a screenshot of the minimal app working properly in Qt 6.7.2, as you can see the entire content of the window takes the full size of the window (i.e. the toolbar isn't present). (The images are also attached)

https://imgur.com/5S6iQoV

Here's a screenshot of the minimal app not working properly in Qt 6.8.0 Beta 2:

https://imgur.com/a/YKV6scI

As you can see, the title bar is present, while it should not be.

Tested on macOS Monterey 12.7.3.