XLSX files come from Microsoft Excel, so you do not have to look for xlsx to excel conversion, you just have to open the .xlsx file using Excel. Of course you can save the spreadsheet to several other formats in Excel, even the previously used XLS format. You can also make templates from the spreadsheets.
But formats from Excel are also supported in many 3rd party alternatives, most notably some of the office productivity suites based on OpenDocument formats, such as OpenOffice or LibreOffice.
Updated: October 11, 2023