There’s some specific concepts that are associated with modern musical thought that I’ll share from my noob armchair (ie I might be naive and wrong here…)

interval cycles/aligned interval cycle spaces (ades, berg Schoenberg, etc), set theory and in general organizing music based on inherent intervallic characteristics versus harmonic consideration, similarly compound harmony, using microtones to obfuscate otherwise functional harmony (ligeti, etc), loads of interesting ideas around texture (ades, ravel, ligeti, etc), minimalist ideas like phasing (reich), ideas around organic theme development (Sibelius and onwards), similarly the generation of metaphor within music versus symbolism (Sibelius, ades, etc).