Sounds to me like they should have done one of those group testing situations or focus groups and watched how people really used their devices. They might have been downloading the file, editing, reuploading. Or copy-pasting from MS Office.

From here:

Denmark has ended a pilot that put the open-source-oriented Collabora office suite in the hands of 38 employees at the ministry responsible for digitalization.

The experience of 38 people! Wow.

No official evaluation comparing Collabora’s performance with Microsoft Office was completed. Reports emerging late last year had already pointed to interoperability issues: documents could display blank pages or lose formatting when opened between the two office suites.

So, stop using OOXML.