Hi Lisa,
I notice that the date in E4 is placed at the left side of the cell, which means it's not recogised by Excel as a date. Based on my test, this is because the region of the site where the workbook is stored (OneDrive for Business or SharePoint Online) isn't English (United Kingdom).
To change the regional settings and fix this, you may refer to the following steps:
If the workbook is stored in your OneDrive for Business:
- Click the gear icon on OneDrive for Business > OneDrive Settings;
- Click More Settings > Regional settings > Locale > switch to English (United Kingdom) > click the OK button.
If the workbook in stored in a SharePoint Online site:
- Click the gear icon > Site information > View all site settings
- Under "Site Administration", click Regional Settings > in Locale, switch to English (United Kingdom) > click the OK button.
Please let us know if there is any update.
Best Regards,
Nathan