I wondered if this was limited to Fairphone / FP4 ? I have a testing build so am prevented from test + comment. Also I barely understand German.
However the app installs, and plays free content fine, and seems to allow registration, although I haven’t actually followed through, on my Moto G(7)Power ocean with
2.6±u-2024xxxxxxxx-community-ocean
It would be strange + interesting if the poor behaviour was one device and build only.
It would seem to merit Report an issue especially if a logcat could be obtained.