Hi Abrasrose,
As per your description, as you did not mentioned your Excel version in your description, first of all please make sure your Office apps are fully updated. The latest version of Office 365 for mac is 16.57. To Check version information, open any Office app, such as Excel, go to the Excel menu and choose About Excel.
If the version appears lower, then manually update Office apps, click Help > Check for Updates from any of the Office app to get the latest build.
For some reason if Office apps still didn’t update, then please download the Update packagefrom this article
Also, try to reboot Mac in safe mode and determine whether background programs are causing the issue. For detailed information, please check this article.
Then, please make sure your file system is OK. starting by checking file system using Disk Utility. If there are file system problems, Disk Utility may be able to fix them.
How to repair a Mac disk with Disk Utility - Apple Support
Disclaimer*: Microsoft provides no assurances and/or warranties, implied or otherwise, and is not responsible for the information you receive from the third-party linked sites or any support related to technology.*
If issue with all Excel files even new created Excel document on your Mac OS, then I suspect components were corrupted somehow. You can go to the Applications folder In Finder and drag Microsoft Excel.app to the trash. Then Restart your Mac Download this installer Install package and use it to reinstall Microsoft Word (the latest version 16.57). Then, restart your Mac and test.
If above suggestion does not work for you, please feel free to confirm your Excel version.
I appreciate your understanding and stay safe!!
Best regards
Waqas Muhammad