When I set the Graphics mode to Hybrid the dGPU stays in active mode. I have to manually select “Integrated” in order to use the iGPU again. Is this a known bug? I went into greater detail in the CachyOS forum:
Hybrid Graphics never switch to iGPU - Issues & Assistance - CachyOS Forum
Hi! As mentioned by the folks in that distribution forum post, what you’re looking for is generally the behavior that “naturally” happens, at least on the devices I’ve used.
I actually had an experience a while back with a gaming laptop where I tried installing extra tools to manage the GPUs like what you mentioned, and ended up just reinstalling the system because I couldn’t make heads or tails of how it was all working 
Posts like this might be helpful in your circumstance: https://www.reddit.com/r/linuxquestions/comments/1im4g7s/nvidia_gpu_draws_power_even_when_idle_under/ - basically, the act of checking the GPU’s state using certain tools could be what’s waking up the GPU.