Why does my FPS drop to 20 when entering crowded city areas?

Entering bustling city areas, my frame rate felt like a roller coaster, dropping from 60 to 20, which was absolutely maddening. I tried setting the fan to full speed in BIOS, but the noise was like a hairdryer in my ear and temps only dropped to 82℃. I used the GamePP Fan Curve Configuration panel to implement a step-up gradient for 65-85℃ and set 90℃ as the full-speed trigger. Core temperatures stabilized at 78-83℃ per HWMonitor, and FPS fluctuations converged to 45-55 per RTSS.