@jmbmkn @libreoffice One of the maintainers behind EuroOffice is Nextcloud (besid IONOS and others). Last year, Nextcloud also switched the standard to OOXML for the Nextcloud-Collabora integration (another Online Office Solution). There was a lot of pushback, but Nextcloud went ahead with it anyway. You can find Nextcloud's position on this topic in the GitHub issue.

https://github.com/nextcloud/richdocuments/issues/4812