This typical for laptops with discrete GPUs. Outputting video over TB can often only be done by the discrete GPU. I do not know the reason why this works this w

This typical for laptops with discrete GPUs. Outputting video over TB can often only be done by the discrete GPU. I do not know the reason why this works this way. On my Lenovo X1E, this is also the case. Thunderbolt video output only works via the nVidia GPU (instead of the Intel graphics on the CPU). So connecting the TB dock causes my fans to spin up, as the laptop is now rendering my desktop using a power hungry nVidia chip.