@bkuhn
The open document format is really a zip file of XML files. You can unzip and diff that?

Maybe diffoscope (from @reproducible_builds) is able to do a diff, too?

@bkuhn
Oh.

I would use conditional markup and linked files for that.

In one of the two spreadsheets, link to the other one as a data source.

Then, create conditional markup so that if the contents of the current cell is different from the cell in that data source, colour the cell red.

This is me saying that without actually testing it, so might not be possible.
@funkylab