Earlier quoted context omitted.
Ideally they should have also told all German banks distribute or offer non-App based accounts or 2FA? But they did not. Also people are dependent on Play or App store. DB does not offer the app for direct download.
Well for banks there is competition (and largeest german consumer bank - Deutsche Bank/Postbank offers a non-smartphone based authentication device [0]). Not so much for government run railway. [0]: https://www.postbank.de/privatkunden/services/online-banking...
If you are that anal then using railway does not need app. You can use a mobile browser or desktop. I have seen people show QR code from their computer too. For D-Ticket one can buy from one of the local transport associations - with Chip Card (I am using that).