A concrete fix inside the September release
Microsoft released KB5124008 on September 8, 2026, for Windows 11 24H2 and 25H2. The official release notes list a correction for unexpected Teams and Outlook closures on Arm64 PCs. The Verge covered the broader Patch Tuesday release that day; the practical focus here is Microsoft’s documented reliability fix.
Which problem it addresses
Microsoft’s release-health record connects the issue to Windows security updates from August 11 onward. Teams and the new Outlook could fail to start or close unexpectedly, particularly on newly installed Arm systems. Classic Outlook and other Office applications were not known to be affected.
That scope matters: this notice does not explain every Outlook crash. TechKili analysis: support teams should compare the affected application, processor architecture and installed update before attributing a user’s problem to this incident.
What to check after updating
The KB5124008 notes also list desktop-personalization and mouse-cursor fixes. For 25H2 and 24H2, the resulting builds are 26200.9445 and 26100.9445 respectively.
Microsoft recommends the latest applicable update in its release-health guidance. For administrators, a useful acceptance check is to confirm the installed build, reopen the affected apps and test the workflow that previously failed. An installed update and a successfully restored user workflow are separate pieces of evidence.