It's the IT support that will be the real problem.
The French gendarmerie managed to do it.
And many companies around the world have managed to do it as well, yes. Look at IBM, for example. The Ministry of Justice in Finland has used OpenOffice for years now, too.
Do you understand what it means
politically when an entire government tries to do it, with tens of thousands of workers currently enjoying pretty high-paid jobs required to completely retrain themselves or get fired?
In Finland, University of Helsinki failed to maintain even student-accessible Linux workstations because of this. Around the turn of the century, they were common (as in entire classrooms full of Linux workstations) in the Faculty of Science (city center and Kumpula campuses), but they just couldn't keep them supported. Students needed them, but as the IT support was separated to
its own unit, they unilaterally chose to no longer support them, citing difficulty of hiring suitable support personnel IIRC. The administration is too far above actual teaching and student needs to understand such decisions, even though they do the huge licensing deals (without actually knowing whether those deals make any sense). The faculty instead decided to offer STEM students a laptop for a tiny bond sum, originally 100€, installed with locally-supported Linux,
Cubbli. I developed the first few versions of the self-registration Debian package, a GUI tool that generated local user accounts based on the University AD details over Eduroam, as a free volunteer, just to support the students and the Linux efforts. The entire university has a bit over 31,000 students, 5,200 academic staff, and about 3,500 non-academic staff, so it's about third of the size of the French Gendarmerie.
In Finland, firing anyone from a government job or non-academic position in an University is almost impossible, due to the labour laws and extremely strong unions here.
"Quiet quitting" usually just leads them being shifted to another department or position, usually with same or higher pay but with fewer duties. It's only taxpayer money, after all. I wonder how many IT support personnel the Gendarmerie had to "shift", "retire", or fire. I suspect it isn't easily done in France either.
One way this can work — noting that I'm not familiar with how the French Gendarmerie did it — is to motivate and train the support personnel
first, years before the transition. You need to go through the IT support administration, and carefully root out the change-fearing maintaintainers-of-status-quo, and basically force or brainwash the administration to be the proponents of the change. (Maybe strongly worded; I do mean careful social engineering and political control.) At the actual user-facing support personnel level, you must show how the change is in their own interests also. And, at the end, those who won't perform in the new system, have to be fired or transferred. I'd be very interested to hear how the Gendarmerie handled all that; it must have been a crucial part.
I know several computational physicists, who absolutely hate open source (calling it always "open sores"), even though they are capable of adapting software tools to their own needs, and occasionally have encountered bugs they had to fix themselves. So, not just "fear" or "phobia" of any unknown thing; just very strong dislike of the entire idea. When the same happened with commercial proprietary software, they are utterly nonchalant about it, because they understood that a commercial company must focus resources where they have the biggest bang for buck. This kind of social, by definition irrational, attitude must not be ignored either. Some are just fanboys and haters, regardless of their capabilities and skills.