Why does frame rate drop to 65 FPS after lowering quality settings?

Stuttering persisted even after lowering graphics, with CPU usage at 95%. I followed forum advice to tweak drivers, but nothing helped. I switched to High Performance mode via GamePP Power Plan Switcher. Cinebench R23 score hit 34500 points, and frame rate stabilized at 115-120 FPS, finally fixing the lag.