[kbit]

In this case, the app itself is in fact open source. The problem is that it relies on a non-free Google/Apple service for detecting contacts. However, I agree: Even such a dependency should strictly be avoided by government apps. This includes not limiting an app to the Play Store and also using alternative channels such as F-Droid.

[nicbou]

The other problem is that it's only available on the German app stores, so if your account is in another country, you can't download the app.

[freemint]

I am aware that it is possible to download this app from other EU countries then Germany.