iPhone 12 pro dead no logo

iPhone 12 pro dead. No sign of damage , bent , or cracks, no liquid damage. After power stock on 0.20 v with power supply. I separated the boards and test again the upper board with poersupply and still same issue. I did diode test on all pins around the upper board and give corrects ohms. I don't have idea what should I do next? If I want to go detail, can I know is there other forum to help me and I learn more.