Can't save Excel files on MacBook

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:

1. Check macOS version Office on Mac should be running on macOS 12 or later.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.

References:

• Unknown Error 0x0 or License not found error in Microsoft 365 or Office running on macOS
• Microsoft Office activation and the Mac App Store
• Fixes or workarounds for recent issues in Excel for Mac
• "Microsoft Excel has encountered a problem and needs to close" when starting Excel for Mac
• Convert from Office 365 to Microsoft Office purchase - Microsoft Q&A
• Word, Excell won't save documents - Microsoft Q&A