[my123]

Optimus proper power management for laptops on Linux (including fully turning the GPU down) only works on Coffee Lake (and AMD Renoir) and later with Ampere or later GPUs.

Prior to that generation, standard power management mechanisms don't work, and so the NVIDIA driver doesn't turn off the GPU when idle on those older platforms.

[FirmwareBurner]

Then https://www.youtube.com/watch?v=OF_5EKNX0Eg

[refracture]

So both the iGPU and Discrete GPUs lacked power management all together, that would explain a lot about how miserable this has been.