I think this is not (entirely) true. Or at least I have some questions:

• Is this an enacted law that I missed? Because it looks like it is a work in progress.
• “All levels of government” Really? We have federalism. I am not sure, if that can be mandated by the governments.

BTW: https://deutschland-stack.gov.de/

I have searched a bit further: For federal and state governments, ODF is binding through IT Planning Council resolutions and federal guidelines, but there is no formal law yet mandating its use. Also, this is not binding for local authorities, but virtual it is.

https://www.it-planungsrat.de/beschluss/beschluss-2025-06