A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data
Hi Rita,
Welcome to Microsoft Community.
Based on the description, it seems like there may have some keyboard issue on your side as normally, Shift+Spacebar will work as Select the entire row in Excel for Mac.
Hence, the first suggestion is to reset the shortcut settings and check if anything will change back. See: Create a custom keyboard shortcut for Office for Mac (microsoft.com)
However, if the issue persists after you reset the shortcut in Excel, please check the following suggestions.
1.Restart Mac in Safe Mode.
This can help us to exclude any possible influences from other third-party apps or background programs that may have a conflict with the Excel app. See: How to use a "clean startup" to determine whether background programs are interfering with Office for Mac (microsoft.com) and kindly refer to the Apple article in the last one to get detailed steps.
2.Make sure you are having the latest version of Excel 16.55 on your Mac. See: Update history for Office for Mac - Office release notes | Microsoft Docs
Feel free to post back and share us the test results for a further troubleshooting.
Best Regards,
Mia