It means that it is de-facto compatible with all operating systems.
Also means that the tooling to make collaborative work in this suite possible already exists because it's a common use case on the web and less so on native software (see Microsoft Office vs. Microsoft 365 online).
Sure, "all" operating systems. "All" that is OSes that have a web browser built for it that at least supports [TransformStream](https://developer.mozilla.org/en-US/docs/Web/API/TransformSt...)... And the browser and spec written and maintained mostly by people outside of France. Kinda compromises the point of being "sovereign" doesn't it?
Forking Firefox whenever the rug is pulled seems doable (with elbow grease), and in the meantime Europeans can invest on problems that don't have an already mature fully open-source solution.