Update, 9 September 2026: Windows fix available
Microsoft has marked the ARM startup issue resolved since 8 September. Windows 11 24H2 uses KB5124008, build 26100.9445; 25H2 uses the same KB, build 26200.9445. For 26H1, Release Health identifies KB5124012. Its individual page was unavailable today, so no target build is stated here. These packages are not interchangeable.
Save open work and back up important data. Check your Windows version and ARM system type; install the current security update offered for your device through Windows Update or your approved IT deployment service. Restart when requested. Check Update history and winver, then test Teams and new Outlook separately. If startup still fails, give IT the build, app version and error message; do not delete profiles.
The Store workaround below remains relevant only to affected devices with updates older than 8 September. It is no longer required for this issue after the matching September update. No independent device test was performed. If a new problem occurs, preserve data and diagnostics first; any system rollback belongs in IT’s existing recovery plan, not a blanket security-update uninstall.
Microsoft Release Health: 24H2 / 25H2 · Microsoft Release Health: 26H1 · KB5124008
Historical status, 7 September — earlier diagnosis and Store workaround
Does your problem match this report?
Checked: 7 September 2026. Following the Windows security updates of 11 August 2026, Teams and new Outlook may fail to start or close immediately on ARM devices. Microsoft lists Windows 11 24H2, 25H2 and 26H1, especially new or freshly imaged PCs without previous Store updates. Classic Outlook, Word and Excel are not covered by this specific issue. This guide uses manufacturer sources, not our own device test.
Identify the system and application first
- Open Settings → System → About. Record the system type, Windows version and OS build. This guide applies to ARM, not every PC.
- Under Windows Update → Update history, check whether the timing matches the August update. Windows 11 24H2/25H2 and 26H1 use different packages; do not compare KB numbers without their version context.
- Distinguish a startup failure from a problem after the application opens, such as mail not arriving. That needs a different diagnosis.
Microsoft’s documented workaround
- Open Microsoft Store on the affected PC.
- Select Downloads → Check for updates. Labels may differ with the Store version.
- Install the latest Auto Super Resolution Package, version 1.0.19.0 or later. A Windows update alone is not the same as this Store package update.
- Open Teams and new Outlook again. Check each separately: the interface must load fully and remain open.
If it does not help
If Store access is blocked, give IT the system type, build and error message. Do not download packages from unofficial sites or delete mail profiles. If the package is missing or no update is offered, record that instead of installing an unrelated package.
Microsoft lists this case as mitigated by a workaround, not permanently fixed by a Windows update. If both applications work, record the result and installed package version. If the failure remains, check the current manufacturer status and investigate other causes.