Merge pull request #5001 from j0shbregman/docs-editor/mac-whatsnew-1757544491

Update mac-whatsnew.md

Author: aditisrivastava07

defender-endpoint/mac-whatsnew.md

@@ -44,6 +44,8 @@ To get the latest features, including preview capabilities (such as endpoint det
 
 ## Known issues
 
+- In version 2506 (101.25062.0005), attempts to upgrade Microsoft Defender for Endpoint on macOS consistently failed.  Other versions of Defender are not impacted. To overcome this issue, there is a supported workaround for supported macOS versions and beta versions of macOS 26.  The instructions for the workaround can be found [here](https://github.com/microsoft/mdatp-xplat/tree/master/macos/upgrade_from_2506_helper).
+
 - Apple fixed an issue on macOS [Ventura upgrade](https://developer.apple.com/documentation/macos-release-notes/macos-13_1-release-notes) and macOS [Sonoma upgrade](https://developer.apple.com/documentation/macos-release-notes/macos-14-release-notes) with the latest OS update. The issue impacts Defender for Endpoint security extensions, and might result in losing Full Disk Access Authorization, impacting the ability of Defender for Endpoint to function properly.
 
 - In [macOS Sonoma 14.3.1](https://developer.apple.com/documentation/macos-release-notes/macos-14_3-release-notes), Apple made a change to the handling of Bluetooth devices that impacts Defender for Endpoint device control's ability to intercept and block access to Bluetooth devices.  At this time, the recommended mitigation is to use a version of macOS earlier than 14.3.1.