Honestly, my traps were built squatting heavy and deadlifting heavy. I’ve done shrugs here and there but almost all of my size comes from squats and deads.
That said, now that I don’t do either of those as heavy, I feel a ton of burn and contraction when I do lateral raises, especially when I hinge forward a bit and hit the rear delts. The key here is to close your mouth, drive your jaw back into your neck (not down), and tilt your head just ever so slightly up.