How to fix 0.3s stutters in Elden Ring Shadow of the Erdtree?

I was so hyped for the Shadow Land, but during huge BOSS fights, the screen would stutter for 0.3s without warning. I first tried dropping graphics to Low, but it only added 3 FPS and made everything look blurry, which was totally discouraging. I then used the GamePP Resource Scheduler to raise the main thread priority to Realtime and killed background updates. RTSS showed frame times converging from 18-40ms to 12-16ms, while AIDA64 tracked memory usage at 7.5-7.9GB and HWMonitor showed 44-50℃.