Pallas
"Modern" is an umbrella term that covers a vast variety of musical styles. I don't really agree on putting all 20th century music in one bucket. Each style has specific challenges.
Ragtime is harmonically very "classical" but the main difficulty is the rhythm, especially the typical ragged syncopation.
Film music is relatively straightforward (once you reach a certain level) because it often has a more transparent texture and lots of repeating patterns, much like the classical era but with more modern harmonies.
Pop is harmonically simple (although unlike rag it uses modern harmonies) but has a lot of rhythmic difficulties. There is rarely a pop tune that doesn't syncopate. Almost all pop is on the off beat (2 and 4) and that is usually emphasized strongly in the LH while the melody is syncopated.
Jazz is hard. Harmonically, melodically, rhythmically. And there's the whole improvisation thing too. Maybe I'll figure it out one day... 😉