Scrolling on the app details works on mine

It works, yes, but for me the scrolling speed seems to not match my thumb, and there's some inertia added — which are both signs that scrolling is hijacked by JS that does its own scrolling instead.

I also find it hard to believe Duolingo Music is free.

The site seems to not have a clear marking for freemium apps. AlternativeTo does that well, they're just marked as 'freemium/proprietary' (or, in rare cases, 'freemium/open-source').