Find out why Excel file tells me I need to upgrade my Mac OS . I am fully up to date.

The message usually appears when the Excel version requires a newer macOS than the one installed, or when macOS is supported but the Office build is too new for that OS.

Key points from current support policy:

1. Microsoft 365/Office for Mac supports only the three most recent major macOS versions.
2. As of September 2025, those are:
   • macOS Tahoe (26)
   • macOS Sequoia (15)
   • macOS Sonoma (14)
3. Starting with the September 2025 update (16.101):
   • macOS Sonoma (14) or later is required to receive updates to Word, Excel, PowerPoint, Outlook, and OneNote.
   • The September 2025 update (16.101) is the last build to support macOS Ventura (13).
   • The August 2024 update (16.88) is the last build to support macOS Monterey (12).

This means:

• If macOS is fully up to date within an older major version (for example, Monterey 12.7.x or Ventura 13.x), Excel can still show a message that an OS upgrade is required, because the major version is no longer supported for newer Office builds.
• The apps may continue to run, but once the macOS version falls outside the supported three-major-version window, Office will no longer receive updates, including security updates.

How to resolve or work around this:

1. Check macOS major version
   • On the Mac, open Apple menu → About This Mac and confirm the major version (e.g., 12 Monterey, 13 Ventura, 14 Sonoma, 15 Sequoia, 26 Tahoe).
   • If it is earlier than Sonoma (14), the upgrade prompt is expected behavior for current Microsoft 365 builds.
2. If possible, upgrade macOS to a supported major version
   • Upgrade to at least macOS Sonoma (14) so Excel and other Office apps can continue to receive updates and stop prompting for an OS upgrade.
3. If the Mac hardware cannot upgrade to a newer macOS
   • The latest Office build that works on that OS must be used:
     • Monterey (12): last supported build is 16.88 (no further updates after that).
     • Ventura (13): last supported build is 16.101.
   • In this case, Excel may still show upgrade messaging when trying to install newer builds, but the installed version will continue to work; it just will not receive new features or security updates.

If Excel is already on a build newer than what the macOS version supports, or if the message persists even though macOS is Sonoma or later, direct assistance from support is appropriate so that the setup and versions can be checked in detail.

References:

• Upgrade macOS to continue receiving Microsoft 365 and Office for Mac updates
• Office running on OS 12.7.6 - Microsoft Q&A
• Office 365 won't install - Microsoft Q&A
• Install MS Office on Ventura OS 2017 Mac - Microsoft Q&A