Yes, you can safely ignore it

The software creates a file on the web server that mimics the Excel file format. The file can generally be opened by any version of Microsoft Excel. However, other programs may have problems opening the file. If you experience this issue here is what to do:…

If you are experiencing issues opening XLS files, we are aware of an issue with Microsoft Office. Microsoft Office in a update in 2016 changed settings during an update. You can view the original details here: https://answers.microsoft.com/en-us/office/forum/office_2010-excel/excel-2010-kb3115322-openin&