Spreadsheets do not come back from a search
The semantic index covers Word, PowerPoint, PDF, OneNote and web pages.
Microsoft’s supported-content list does not include .xlsx. Copilot
still works on a spreadsheet you open or attach, but retrieval across
spreadsheet files is not what the index is built for. For a firm that runs on
Excel that is material, and it is on the table before there is a licence decision
to make.