The materials I downloaded from Quixel Bridge have only a material instance and several textures, so where can I find the original material blueprint for that material instance?
Megascans assets do not use Blueprints. They’re using master materials. You can find the master material for each instance by opening the instance and scrolling down to the parent material, then opening it.
No you don’t, because when you download the texture it creates a material instance but no parent. So you can’t just get it, it’s blank as shown above.