docs: document change in draggable region behavior on macOS (#37408)

Co-authored-by: trop[bot] <37223003+trop[bot]@users.noreply.github.com>
Co-authored-by: Jeremy Rose <nornagon@nornagon.net>

docs/breaking-changes.md

@@ -14,6 +14,14 @@ This document uses the following convention to categorize breaking changes:
 
 ## Planned Breaking API Changes (23.0)
 
+### Behavior Changed: Draggable Regions on macOS
+
+The implementation of draggable regions (using the CSS property `-webkit-app-region: drag`) has changed on macOS to bring it in line with Windows and Linux. Previously, when a region with `-webkit-app-region: no-drag` overlapped a region with `-webkit-app-region: drag`, the `no-drag` region would always take precedence on macOS, regardless of CSS layering. That is, if a `drag` region was above a `no-drag` region, it would be ignored. Beginning in Electron 23, a `drag` region on top of a `no-drag` region will correctly cause the region to be draggable.
+
+Additionally, the `customButtonsOnHover` BrowserWindow property previously created a draggable region which ignored the `-webkit-app-region` CSS property. This has now been fixed (see [#37210](https://github.com/electron/electron/issues/37210#issuecomment-1440509592) for discussion).
+
+As a result, if your app uses a frameless window with draggable regions on macOS, the regions which are draggable in your app may change in Electron 23.
+
 ### Removed: Windows 7 / 8 / 8.1 support
 
 [Windows 7, Windows 8, and Windows 8.1 are no longer supported](https://www.electronjs.org/blog/windows-7-to-8-1-deprecation-notice). Electron follows the planned Chromium deprecation policy, which will [deprecate Windows 7 support beginning in Chromium 109](https://support.google.com/chrome/thread/185534985/sunsetting-support-for-windows-7-8-8-1-in-early-2023?hl=en).