I don’t know the BIOS of that model. Some can enable both GPUs or just one … some enable those automatically when set to IDG and there is a dGPU (PCIe graphics card) with a monitor connected, but in that case you can’t have a
/etc/X11/mhwd.d/nvidia.conf because that will get priority when booting in linux, but will fail, as already happen to you, because you had no Display connected to it as you connected it to the iGPU. That is how
video-hybrid-intel-nvidia-455xx-prime comes into play if you want to go that road.
Another way is to keep
video-nvidia-455xx but remove the
/etc/X11/mhwd.d/nvidia.conf if BIOS is set to IDG, so both GPUs work, otherwise the iGPU will fail because the nvidia will hijack xorg, but because what i explained above, the lack of a Display connected when you installed the driver, as was connected to iGPU, the config is not proper, hence will also fail even if you now connect the Display to the dGPU.