There are a few different ways to close all open workbooks in Excel. One way is to click on the File tab, then click Close All. This will prompt a dialog box to appear asking if you want to save any changes you've made; click Yes, then click OK.

Another way to close all open workbooks is to use the keyboard shortcut Ctrl+Shift+F4. This shortcut will also prompt a dialog box asking if you want to save any changes; click Yes, then click OK.

If you have a lot of workbooks open and you want to close them all at once without being prompted to save changes, you can hold down the Shift key while clicking on the File tab, then clicking Close All. This will close all workbooks without saving any changes.