Sounds like a synth to me. A couple key ingredients here:
Oscillator 1: Square. Usually these subby basses are Saws, but the use of Square makes this bass a little different
Oscillator 2: Sine, 1 octave up. For those higher notes this won’t make as much of a difference. But for those really low farty notes, the Sine will add body
Filter: Low pass, 24 dB. Turn the Cutoff pretty far down, and then give it some Drive for saturation and warmth
Amp Envelope: A little bit of Release, somewhere around 200 ms. This is one of those very subtle changes that makes the sound feel bigger/fatter.
Voices: Mono