This usually means Office on the Mac is no longer recognizing the installed license, so the apps fall into reduced functionality mode. In that state, apps can open files but may not allow editing or saving.
Try these steps in order:
- Check macOS version
Office on Mac should be running on macOS 12 or later.
- Update Office first
If Office was installed from Microsoft:
- Close all Office apps.
- Open Finder > Applications > Microsoft AutoUpdate.
- If needed, check /Library/Application Support/Microsoft/MAU2.0/.
- Install Update All.
If the apps were installed from the Mac App Store:
- Close all Office apps.
- Open App Store > Updates.
- Update the Microsoft apps.
- Sign out and sign back in with the licensed account
If the wrong account is signed in, Office can show the wrong license type and disable save/edit features. Sign out of Office, then sign back in with the Microsoft account associated with the Office Home & Student 2021 purchase.
- If the apps still show the wrong license, remove and reinstall Office
This is the most direct fix when a perpetual license install has been replaced or is being treated like a Microsoft 365 install.
- Close Word, Excel, PowerPoint, and Outlook.
- Open Finder > Applications.
- Control-click the Office apps and choose Move to Trash.
- Reinstall using the Microsoft installer for the purchased version, not the App Store version.
- If saving still fails after reinstall, test in a new macOS user account
- Go to Apple menu > System Preferences > Accounts.
- Create a temporary test account.
- Sign in to that account and open Excel.
- If saving works there, the problem is likely limited to the original macOS profile.
- If Excel itself is unstable, reset Excel preferences
- Quit all Office apps.
- In Finder, go to Home > Library > Preferences.
- Move
com.microsoft.Excel.plist to the desktop.
- Test Excel.
- If needed, also check Home > Library > Preferences > Microsoft and move
com.microsoft.Excel.prefs.plist to the desktop, then test again.
The most likely cause in this case is that the Office 2021 license is no longer being matched to the installed apps, which is why Excel shows as not activated and Save is grayed out.
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