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.
This track was made using Serum.
Instrument Tremolo Ambience
Sample pack Sickrate & SIIK Essentials II - Full Pack
Loop name SSE2 Tremolo Ambience 07 - D#