@HonkHase comment on Hacker News: "German implementer here. We have to use some kind of attestation mechanism per the eIDAS implementing acts. That doesn't work without operating system support.
The initial limitation to Google/Android is not great, we know that, and we have support for other OSs on our list (like, e.g., GrapheneOS). It is simply a matter of where we focus our energy at the moment, not that we don't see the issues."

https://news.ycombinator.com/item?id=47647522