So when I use HWinfo to view the sensors, under the MOBO mainboard it shows my temp of 37c during RDR2. At that time my CPU (Ryzen 5 3600) is running anywhere from 55c to 66c. My GPU (EVGA GTX 1060 6gb) is running 69 to 73c. Im new to PC and this is my first build.
OK...so yeah, MOBO is probably a motherboard sensor, if anything. If lucky it might be picking up the air flow coming out of the GPU and can be used to ramp up case fans when the GPU starts working hard.
But it's well after the GPU so it probably doesn't move a lot. You can test it by checking it running a GPU-only stress, something like Valley, and watch how much it changes after 5-10 minutes. It will not likely ever read as hot as the GPU itself.
On my motherboard it will move from 35C to 41C when the GPU's in the middle of Valley, barely enough to ramp up fans reliably.