How do I fix frame rate fluctuation in Expeditions: Rome on a Vastarmor RX 9060 XT?

Combat felt jittery with FPS fluctuating between 60-75. Switching to High Performance failed due to background interference. I used GamePP Power Switcher to disable processes and lock the plan. FPS stabilized at 80-85, and core temperature dropped to 76-82℃, confirmed by 3DMark.