It seems like a lot of european countries have started becoming more concerned with digital sovereignty and some have begun enforcing using open formats like ODF / ODS

I’m struggling to find support though. A lot of software seems to open ODS files but force the XLSX format on save.

I’d expect something like OnlyOffice to have support since it’s used by the French government and the government of their German neighbours is enforcing ODS usage + there should be a reasonable library they could import to make it work without a large overhead