Fix Excel Online Data Validation Drop-Down Missing in Some Cells

Open the workbook in Excel Online and click on a cell where the data validation drop-down arrow is missing.

Navigate to the Data tab on the ribbon and click on the Data Validation icon.

Review the formula in the 'Source' field. If it uses complex named ranges or dynamic arrays, replace it with a direct, absolute cell reference (e.g., =$A$1:$A$10).

Click OK to apply the changes, refresh the page, and check if the drop-down arrow reappears.

Find a cell in the same row, column, or sheet where the data validation drop-down arrow is functioning correctly.

Select the broken cell and check the Home tab to see if it is merged. Merged cells frequently cause rendering errors in Excel Online. Click 'Merge & Center' to unmerge it if necessary.

Select the working cell, click the Format Painter tool on the Home tab, and then click the broken cell to apply the exact same formatting properties.

Record your Microsoft Office version, browser details, affected file samples, and take screenshots showing the missing drop-down arrows.

Reach out to your organization's Microsoft 365 Administrator and provide them with the gathered information.

Ask the administrator to log into the Microsoft 365 Admin Center and open an official support ticket detailing the tenant-wide Excel Online issue so the service team can investigate.