Munich started using open source a while back. Must be more than 15 years ago now. As far as I know, they still do, but I reckon I read something about how they had to get a couple of computers going on Windows for specific purposes.
I believe Munich wasn't the only place, but I'm not sure.
Because of this
Microsoft Technology Centre Munich
Microsoft was really not very amused at all that the city in which they have one of their major european centres (and no doubt pay a not insignificant amount of tax) chose to move away from Microsoft products. I heard on the grapevine that Microsoft made "special deal" offers worth millions to try and stop the City of Munich from making the move. Didn't work... 😀
EDIT: Just found this Wiki article
Ende November 2017 wurde vom Stadtrat beschlossen, das Projekt zu beenden und alle Rechner bis zum Jahr 2020 auf Windows umzustellen.
"At the end of Nov 2017, the City Council decided to end the (LiMUx) project, and revert all the computers in the city administration back to Windows by 2020."
What a pity. I would attribute that to changes in the politics and politicians on the council, and no doubt hard lobby work by microsoft.
Elswhere the article there is mention of problems in the project caused by poor comunication between various departments in the administration. That is highly llikely possible. During the time I was in Munich, I was periodically astonished at how little the various offices and departments appeared to communicate with each other. Sometimes quite obviously not at all.