Reduced Frames when Gaming

Whenever I play a graphically demanding game on my Razer Blade 15 laptop, for example Rust, I can play with solid 60+ FPS for around 5-10 minutes, with my CPU usage being around 30-40% and my GPU usage at around 60-70%. I have an Intel i7-10750H CPU @ 2.60GHz CPU, and a Nvidia GTX 1660ti GPU. After about 10 minutes, my GPU usage shoots up to 99/100% usage with the clock speed dropping to roughly 300MH and my CPU usage decreases to about 10% with normal clock speeds. My FPS now becomes 15-20. Originally, I thought it might be thermal throttling as my computer sits at around 40-60C when doing average tasks, but shoots up to 90-100C when gaming, but after reducing the power input to the CPU, there is no more thermal throttling according to XTU, but the issue still occurs. My computer is fully updated, and I have had it for about a year. Does anyone know what I can do to fix this issue?