Excel is not working on my MacBook Air with High Sierra

Please be more specific. To merely say "but it's not working" is not information we can respond to. It would help to know what the computer's operating system is and exactly what version of Microsoft Office you are running. I am thinking that you may be trying to open files with a 32 bit Excel app when your OS only runs 64 bit apps. Otherwise, you should go to the Microsoft help forum, since it is their product.

Look into the Free LibreOffice, it handles MS Office files like Word & Excel, & Page Layout…

https://www.libreoffice.org/

And thanks to VikingOSX…

Let's not overlook SoftMaker's Office 2021 suite which has familiar Word and Excel UI design, and opens these documents in their native formats.