We sincerely apologize for the delay in notifying you of this issue regarding Microsoft 365 apps being unavailable on macOS devices.
For details on this issue and how to address it, please refer to our FAQ page.

■ Overview
The digital certificate used for license authentication of Microsoft 365 apps expired on July 13, 2026, which may cause Office apps to suddenly become unavailable. This issue affects macOS devices only; Windows devices are not affected.

■ Affected Conditions
This issue is believed to occur when Microsoft 365 apps have not been updated to the latest version. Regardless of your OS version, you may be affected if you are using an app version older than the following:
・Microsoft 365 app version earlier than 16.83

■ Resolution (for macOS 14 or later users)
In most cases, the issue can be resolved by following "3. Reinstalling Microsoft 365" in our FAQ.
FAQ: Office (Microsoft 365) suddenly stops working on macOS devices with error "Unknown Error (Error Code: 0x0)."

■ Important Notes (for macOS 13 or earlier users)
The current system requirements for Microsoft 365 cover the three most recent versions of macOS (macOS 14 Sonoma, macOS 15 Sequoia, and macOS 26 Tahoe). Therefore, reinstalling Microsoft 365 is not possible on macOS 13 or earlier. In addition, Kyoto University's security policy recommends upgrading your OS, as continuing to use an OS that has reached end of support poses security risks from the perspective of maintaining the safety of information assets. We kindly ask that you upgrade to macOS 14 or later, and if upgrading is not feasible, please consider purchasing a new device.

We sincerely apologize for any inconvenience this may cause, and we kindly ask for your understanding.