one of the advantages of LibreOffice is that the format is ISO-standardised and truly open.

In my opinion I wouldn’t consider paywalled ISO standards as “open”. But maybe these ones are available for free.

That has not been the case for any of the ISO standards I have needed. Maybe I have been doing it wrong. Or do you think maybe they don’t realize they probably spend thousands of dollars to get access to those “open” ISO standards.