Might just be my area then (Berlin) I hardly see job ads for JS on the backend.

Wow we must be in separate Berlins because I see tons of JS backends. My impression is Javascript & Python are competing for most popular backend.

Seconded that in another comment in this thread. Lots of "fullstack JS saves you money since you can hire the same devs for web, backend & mobile" in Berlin, with varying success

Quite possible that I live in my bubble! I see a lot of React & React Native but hadn't seen so much on the backend.

Node is massive in London so, yes, your experience has an element of local bias.