Hello,
Thank you for coming to the forum, my name is Fuad, and I will be happy to assist you in the best way I can.
Many of the updates require that you are using the latest OS to clear out the bugs. That is my experience with MAC.
I will advise and so will many that you do the update.
What else you can try is to reinstall the Excel app, via the steps below:
Open Finder > Applications > scroll down to Microsoft Excel and select it to move to trash by Ctrl+click
Then in Finder again: In Finder, press COMMAND+Shift+g. In the window that opens, enter ~/Library and then click Go.
Open the Containers folder and Ctrl+click Microsoft Excel and Move to Trash (if you do not see Microsoft Excel, do not worry)
Restart your MAC to complete the uninstallation
Then go to App store and download another Microsoft Excel.
I kindly await a reply for a follow-up
Best R