https://github.com/MinBZK/mijn-bureau-infra/
They show all the components they use here https://minbzk.github.io/mijn-bureau-infra/docs/category/com... and have set up guides for departments to operate it all on Kubernetes
I'm guessing from my own use of NextCloud, Matrix etc that this will simply be deemed not good enough compared to Google Workspace or Microsoft WhateverItsCalledNow as these things are pretty rough around the edges in my experience, but this looks like a good step in the right direction to me