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.
Intro and Breakdown are based around a guitar loop I've found, most of the leads and basses are serum, sylenth1 and spire! The Piano chords are made with free vst LABS!
Sample pack REV-GE2 Muted Guitar Loop 03 F#maj (128 BPM)
Loop name Revealed Guitars Pack