Hi Matt,
Thank you for posting your question in this community. based on your description and screenshot, you found that the Filter feature is not working correctly in Excel for the web app, but the same file works fine in Excel desktop app.
I also did a test from my side, which I open an Excel file in Excel for the web app in browser from a SharePoint document library. The filter can be applied correctly in workbook.
To further narrow down this problem, may I confirm the following information at your convenience?
1: Does this scenario occur in all your Excel workbook in SharePoint site or this Excel workbook only?
2: How about the Excel file in different SharePoint site? Does the filter work?
3: How about the other colleagues in your organization? When they open this workbook in Excel for the web, is the filter working correctly?
At meantime, try to switch to a different web browser and InPrivate Window, such as Microsoft New Edge and see whether the same scenario occurs.
Best regards,
Dihao