Provide clear user guidance when uploading XLSM files

We're encountering issues with our file processing system when users try to upload XLSM (macro-enabled) Excel files. Currently, our package can't handle these macro files, which creates a poor user experience.

What we'd like to see implemented is a user-friendly message that appears when someone attempts to upload an XLSM file, instructing them to reformat the file as an XLSX file instead. This would provide clear guidance rather than leaving users confused about why their upload failed.

Our team noted that we now have the infrastructure to convert from effectively any Excel format to .xlsx using libreoffice, which we recently shipped. This capability means we could potentially support XLSM files directly by converting them on the backend. The implementation would take approximately one day of development work.

The ideal solution would either:

• Automatically convert XLSM files to XLSX format during upload

• Display a helpful error message guiding users to save their file in XLSX format