how do i open an xlsb file

This is an ancient Microsoft Excel Binary file format discussed in more detail here. This format was released back in 2006/2007 timeframe as an alternative format to the emerging XLSX standard with Office 2007.

If you do not have a new (16.52) version of MS Excel, then download the free LibreOffice 7.2+ as it supports the Microsoft Excel XLSB document format. Once opened in LibreOffice Calc, you can resave it as a current Excel XLSX document an be done with archaic formats. I very much doubt that Apple's Numbers 11.1 spreadsheet can open the XLXB format.

Errata: Meant to say XLSB, not XLXB in last sentence.

Great info! :)