Teams and the new Outlook fail to launch on Arm Windows 11 PCs after KB5121003 (September 1, 2026)
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TL;DR
On Arm based Windows 11 PCs, Microsoft Teams and the new Outlook for Windows either fail to launch or close unexpectedly after the security updates released on or after August 11, 2026, and Microsoft opened a known issue for it at 18:46 PT on September 1, 2026, recorded on Microsoft Learn. Classic Outlook, Word and Excel are not affected, which is why this looked like an app fault rather than an update fault. There is a workaround, a Microsoft Store package, and no update side fix as of September 1, 2026.
- The known issue opened at 18:46 PT on September 1, 2026. It is the first vendor statement that a Windows update, not Teams or Outlook, was behind the launch failures.
- Originating updates: KB5121000 on OS build 28000.2704 for Windows 11 26H1, and KB5121003 on OS build 26100.9168 for 25H2 and 24H2, both dated August 11, 2026.
- Microsoft names Surface Pro 11 and Surface Laptop 7, and says the issue is most likely on new or freshly imaged PCs that have not yet installed any Microsoft Store updates.
- The workaround is installing Auto Super Resolution Package version 1.0.19.0 or later from the Microsoft Store. It costs a download and does not require removing the security update.
- Only Teams and the new Outlook are listed. Classic Outlook, Word, Excel and other applications are not known to be affected.
What Microsoft acknowledged on September 1
Microsoft's entry says that after installing security updates released on or after August 11, 2026, Microsoft Teams and the new Outlook for Windows might fail to launch or close unexpectedly on Arm based devices. The scope line is the useful one: "Classic Outlook, Word, Excel, and other applications are not known to be affected."
The second line explains the shape of the reports: "This issue is most likely to occur on new or freshly imaged PCs that have not yet installed any Microsoft Store updates." So the people most likely to meet this are the ones unboxing a new Arm laptop, or finishing a fresh image, at the moment they open their mail and their meetings.
The updates and devices involved
Microsoft's 25H2 and 24H2 known issues page carries the same entry, opened at 18:46 PT on September 1, 2026, and names Surface Pro 11 and Surface Laptop 7 among the affected devices, per Microsoft Learn. The affected platforms are Windows 11 26H1, 25H2 and 24H2, with no server editions listed.
Three weeks passed between cause and acknowledgment: the updates shipped on August 11, 2026 and the known issue opened at 18:46 PT on September 1, 2026. For most of that stretch the failure looked like an app problem, which is the next section.
| Windows version | Originating update | OS build | Released |
|---|---|---|---|
| Windows 11 26H1 | KB5121000 | 28000.2704 | August 11, 2026 |
| Windows 11 25H2 and 24H2 | KB5121003 | 26100.9168 | August 11, 2026 |
Why this looked like an app problem
Teams and the new Outlook are Store delivered apps. When those two refuse to start while Word and Excel open normally, the natural conclusion is that the apps are broken, and the troubleshooting goes at the apps. Microsoft's scope line is what redirects it, because a fault that spares classic Outlook, Word, Excel and other applications but takes both of those is not an app fault.
The workaround points at the same seam: it is a Microsoft Store package, not a Windows patch. Microsoft has published no root cause, and I am not going to infer one from the name of the package.
The workaround is a Store package, not an uninstall
Microsoft's published workaround is to open the Microsoft Store, choose Downloads, then Check for updates, and install the latest Auto Super Resolution Package, version 1.0.19.0 or later.
The cost here is unusually low for a Windows known issue: a download, and nothing else. You do not have to remove the August security update, which matters, because KB5121003 and KB5121000 are security updates and rolling them back to make Teams start would trade a launch failure for an unpatched machine. As of September 1, 2026 no Windows update resolves this, so the Store package is the whole of the remedy.
Also on September 1
Separately, Windows Latest reported on September 1, 2026 that Microsoft was rolling out a fix for Windows 11 restarting for updates more often than it needed to, with Microsoft describing the old behavior as more interruptions than necessary. That one moves in your favor and needs nothing from you.
What you can do today
1. Establish whether the PC is Arm based. Surface Pro 11 and Surface Laptop 7 are the two devices Microsoft names. If the PC is not Arm based, this entry is not your problem.
2. Open the Microsoft Store, choose Downloads, then Check for updates, and let the Auto Super Resolution Package reach version 1.0.19.0 or later. Then start Teams and the new Outlook again.
3. Do not uninstall KB5121003 or KB5121000. They are the August 11, 2026 security updates, and the published workaround does not ask you to remove them.
4. On a new or freshly imaged Arm PC, run the Store update pass before you conclude anything is broken. Microsoft says that is the population most likely to hit this.
5. If the apps still fail once the package is at 1.0.19.0 or later, write down the OS build from winver and the package version, and treat it as a separate report. Microsoft's entry covers the launch failure the package addresses and nothing wider.