A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
The desktop versions of Excel provide a Move or Copy feature which enables 1 or more selected sheets to be saved to a new or to a different workbook file. AFAICT, Excel Online does not have a comparable capability... According to the Excel Online Help:
Can I copy a worksheet to another workbook?
Copying a worksheet to another workbook isn’t supported in Excel Online. Learn more about doing this or about using Excel desktop application instead.