A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
Hello Sean,
Welcome to Microsoft Community and thank you for posting your query.
Start Excel application in safe mode, create new spreadsheet with data validation and check if it works as expected.
- Press the ‘Windows + R’ key on the keyboard.
- In the ‘Run’ window type Excel /safeand press ‘enter’. Note: there is a space between the word Excel and the /
If Excel works as expected in application safe, then disable the add-in(s) by following the steps below and verify the status.
If issue persist, try repairing Office suite using the following link and check if data validation in Excel work as expected.
I hope the above information helps. Let us know if you need further assistance.
Thank you.