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.
made this track from this trumpet loop from splice, pitched it up, made it faster to 118 bpm and build the entire track around it.
Sample pack fireplace
Loop name PJ_FP_Composition_loop_10_Composition_78BPM_Am