The base is original from the producer (chords and melodies), but is complemented with elements that complement the song that come from samplepacks, usually, vocal chops, guitars, wobbles sections, glitch effects. It is the standard in which most of producers work, in a project you will find MIDI files made by the producer, but also melodic loops.
Several layers of deep key stabs, and pads that are creating the atmosphere
Sample pack Ableton Spectral Textures
Loop name RareRoads-140bpmDM