Melodies In Non-Functional/atonal Music

Hey everyone! Long time lurker.

been learning a lot about Tonal Harmony and am slowly getting into more crazier later stuff (romantic period and whatnot)

Unfortunately in the literature I have looking at though mostly focuses just on the harmony, and Im kindof confused when it comes to the later stages just how melodic content is formed.

I guess what I'm wondering is what kind of considerations do you take(or NOT take) when you aren't following a tonal idiom. How are passing notes and suggestions for using chord tones changed(if at all) when dealing with "chords" that are based on sonority or a tone row ?

is there any good literature that delves into this? most harmony books I have looked at only seem to touch briefly on the 20th century stuff

thanks in advance!