They need to focus on archaic government processes which rely on document formats that require proprietary software to view properly, while good open source software for the same task exists. And where lacking, focus on improving open source support for a particular task.

A good start would be to cut use of this OOXML Transitional format entirely. Default to LibreOffice's default formats, and (perhaps) support OOXML Strict where it helps transition.

That way any government employee saving their work in OOXML Transitional or other proprietary format, would automatically stick out as a dumbass who failed to do their job. Pass documents that are published through some validators / allowed-format checkers, and the public only gets stuff that's viewable with software of their choosing.

None of this is hard. It's mostly about changing defaults & a bit of employee training.