### Preflight Checklist

- [X] I have read the [Contributing Guidelines](https://github.com/electron/electron/blob/main/CONTRIBUTING.md) for this project.
- [X] I agree to follow the [Code of Conduct](https://github.com/electron/electron/blob/main/CODE_OF_CONDUCT.md) that this project adheres to.
- [X] I have searched the [issue tracker](https://www.github.com/electron/electron/issues) for a feature request that matches the one I want to file, without success.

### Electron Version

14.0.0

### What operating system are you using?

macOS

### Operating System Version

macOS Big Sur 11.6

### What arch are you using?

x64

### Last Known Working Electron version

13.5.2

### Expected Behavior

When I set the `vibrancy` option on a new BrowserWindow (e.g. to "popover"), the window's background should reflect this.

<img width="838" alt="CleanShot 2021-10-18 at 22 25 54@2x" src="https://user-images.githubusercontent.com/541628/137801784-5ba70aba-40c0-4dec-a112-d770d7db24ec.png">
 

### Actual Behavior

The window's background stays white. Adding `transparent: true` to the options makes the background work as expected but removes the title bar.

<img width="820" alt="CleanShot 2021-10-18 at 22 26 48@2x" src="https://user-images.githubusercontent.com/541628/137801905-ad88db6f-2aa7-4f42-bb15-829eb2581fa4.png">

<img width="827" alt="CleanShot 2021-10-18 at 22 28 01@2x" src="https://user-images.githubusercontent.com/541628/137802078-0b7854fe-4de1-49d5-8d44-18cf78b3739a.png">


### Testcase Gist URL

https://gist.github.com/bbc333443f77ce4a6061d43eddf67fd4

### Additional Information

This might be related to #30993 
shell/browser/api/electron_api_browser_window.cc
BaseWindow::ResetBrowserViews();
  BaseWindow::AddBrowserView(value);
#if defined(OS_MAC)
  UpdateDraggableRegions(draggable_regions_);
#endif
}
void BrowserWindow::AddBrowserView(v8::Local<v8::Value> value) {
  BaseWindow::AddBrowserView(value);
#if defined(OS_MAC)
  UpdateDraggableRegions(draggable_regions_);
#endif
}
void BrowserWindow::RemoveBrowserView(v8::Local<v8::Value> value) {
  BaseWindow::RemoveBrowserView(value);
#if defined(OS_MAC)
  UpdateDraggableRegions(draggable_regions_);
#endif
}
void BrowserWindow::SetTopBrowserView(v8::Local<v8::Value> value,
                                      gin_helper::Arguments* args) {
  BaseWindow::SetTopBrowserView(value, args);
#if defined(OS_MAC)
  UpdateDraggableRegions(draggable_regions_);
#endif
}
void BrowserWindow::ResetBrowserViews() {