CPU temp ONLY controls both CPU and GPU fan speed.
When CPU is 70C and GPU is 40C, GPU fan speed increases tho it shouldn't.
When CPU is barely used, maybe 50C (Benching GPU, Unigine Superposition 1080P EXTREME), GPU fan speed isn't raised at all.
It has been like this since I got my Strix in early february 2021.
Asus ROG Strix G17 G713QR-HG022T, BIOS 315
Uploaded a video where I stress CPU and fan speeds are shown (maximize the video)
Why shouldn't? Don't you think that the GPU fan may help in overall temp decrease? Both fans are in the same chasis and doing their job together.