If you’d like to draw a line through data in a cell to maybe show edits or completed tasks, the font strikethrough option isn’t available in Excel Online.
If you have the Excel desktop application, you can use it to open your workbook and apply the strikethrough formatting there. Here’s how:
Click Open in Excel.
Select the cells containing the data you want to format.
Click the Format Cells box launcher.
Tip: You can also press Ctrl+5.
In the Format Cells box, under Effects, click Strikethrough.
Save the workbook and reopen it in Excel Online to see the changes.
For news about the latest Excel Online updates, visit the Microsoft Excel blog.