There is only one file type that uses the .XLSHTML extension:
Microsoft Excel HTML Spreadsheet
An XLSHTML file is an HTML version of a spreadsheet created with Microsoft Excel, a spreadsheet productivity application. It contains the HTML representation of the source .XLS spreadsheet file, and is typically published online to be viewed in a web browser.
Microsoft Excel no longer supports the XLSHTML format. Instead of saving spreadsheets as XLSHTML files, you can now save them as .MHTML and .MHT files, which are more widely supported.
To create a webpage version of your document in Excel 365, select, then choose the "Single File Web Page (*.mht, *.mhtml)" option from the dropdown menu. You can also choose to save your document as an .HTM or .HTML file.
Unfortunately, there are no known applications that fully support the XLSHTML format since Microsoft Excel dropped support for it.
Updated: February 10, 2021