Hi SLG75,
Welcome to Microsoft Community.
If you prefer to work with your data in Excel Online, you can format the cells as Date, then double-click a cell to enter edit mode, which will trigger the built-in date picker in Excel Online. This date picker is a browser-based feature developed by Microsoft.
If you would rather use a native Date Picker add-in in the Excel desktop application, it is available in the 32-bit version of Excel (Developer>Insert>More Controls>Microsoft Date and Time Picker Control 6.0).
For the 64-bit version of Excel, a more suitable option with a more visually appealing interface is a third-party add-in from the Excel Add-in Store. I recommend Mini Calendar and Date Picker add-in, which can be downloaded directly from the Excel Add-in Store.
Once the add-in is enabled, a small window will appear above your worksheet. Simply click on a date, and it will be inserted into the selected cell.
I hope the information above is helpful to you. If you have any other questions or want to share more context, please let me know in your reply!
Best Regards,
Thomas C - MSFT | Microsoft Community Support Specialist