Why does Hitman 3 drop from 70 to 20 FPS in complex maps?

The moment I entered a top-secret area, the frame rate plummeted from 70 to 20 FPS, making the game feel like a slideshow. I tried limiting the GPU maximum power to 80% via software; while the drops stopped, the loss in visual detail was unacceptable and left me speechless. I then used the GamePP Power Plan Switcher to set the system to Ultimate Performance and enabled enhanced Load-Line Calibration in the BIOS. In 3DMark stress tests, voltage fluctuation converged from 0.5V to 0.1V, and GPU temperature remained stable at 65-72℃ per GamePP.