I recommend the novel " Super Civilization Evolution Overlord " to you. It's a sci-fi novel about evolution and mutation. Its main character had obtained a feudal lord system, and his current level was the prehistoric civilization. He could only have a small territory in the real world and head to the prehistoric world. The real territory would collect energy, and the prehistoric world would complete the conquest mission. Among them, the protagonist also discovered a magic crystal mine, which could be used to exchange for very useful items with the NPCs in the mine. I hope you like the feudal lord theme and sci-fi elements of this novel.