I tested the spreadsheet component, and for me it works as expected — it produces a normal .xlsx file. In short, an XLSX file is actually a zipped archive containing a set of XML files. If you're seeing it as an archive, it may indicate that you don't have a program like Microsoft Excel, LibreOffice Calc, or Numbers (on macOS) installed to open it properly.
If that's not the case, could you please extract a sample from your code that reproduces the issue and share it via https://blazorrepl.telerik.com/ ?
Setting thefilename in the OnDownLoad Event solves the issue.
I guess there's no default file anymore