alt Hacker NewsUsing an ID card reader is already possible. See here for a list of Linux repos supporting German IDs: https://www.ausweisapp.bund.de/en/open-source Finding a working hardware/software combination for your ID card is up to you.
The app is an alternative for people who don't want to buy or carry around a card reader, but who already have a smartphone.
It is possible for e-signatures and similar variants. However, there is no sign that the "age verification" will support this variant. If you go to the demo <https://cinema.ageverification.dev>, no option is given other than the Android/iOS app.
So it seems that the app is only an alternative in the case of government portals, but it is not an alternative for "age verification".