I have tried to add multiple excel spreadsheets to ArcMap 10.8. Whenever I try I get the message below. How can I fix this?
I'm guessing they are xlsx post 2007? resave them as xls if possible.
David has a point. If you have not added the 2007 Office drivers, an xlsx file is not readable in ArcMap.
This link addresses the .xlsx format:
Understanding how to use Microsoft Excel files in ArcGIS—Help | Documentation