To set Microsoft Excel as the default spreadsheet program on a Mac, follow these steps:
Open a Finder window on your Mac.
Find a file with the .xlsx or .xls extension (an Excel file) on your computer.
Right-click (or Control-click) on the file and select "Get Info" from the context menu. Alternatively, you can select the file and go to the "File" menu at the top of the screen and choose "Get Info."
In the Get Info window, find the "Open with" section.
Click on the dropdown menu next to "Open with" to see a list of available applications.
If Excel is already listed, select it from the list. If Excel is not listed, click on "Other" and navigate to the Microsoft Excel application. It is typically located in the "Applications" folder.
Once you have selected Excel, click the "Change All" button below the dropdown menu. A confirmation dialog will appear.
In the confirmation dialog, click "Continue" to set Excel as the default application for all files with the .xlsx or .xls extension.
From this point on, Excel should open as the default program whenever you double-click on an Excel file or when you open Excel files from other applications.