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I installed Kubuntu 18.04 in a new Lenovo Ideapad 330; some of those have Intel UHD Graphics as well as the NVIDIA GPU. I chose to use Kubuntu alongside the default Windows 10 installation since, after a lot of tries with Ubuntu 18.04, it was not installing correctly and gave some problems. That may be why Ubuntu is not a supported OS per Lenovo.

The PC's temperature seems normal in Windows 10 (while playing some Gamecube video games on the Dolphin emulator, which I suspect does not overheat the GPU), but when running Kubuntu, even just editing in gedit or web browsing, it gets abnormally hot; not enough to auto-shutdown, but enough to notice a clear difference between Windows and Linux. This overheating is not normal at all (software related 99%)

I took a look on forums and so on, and read that installing dedicated drivers (NVIDIA ones) instead of the default ones that come with the Kubuntu distro might be a solution for this, so I downloaded the drivers (the GPU is an NVIDIA GEFORCE GTX 1050) from NVIDIA When I tried to install the drivers, I got an error message discussed in post How to unload kernel module 'nvidia-drm'?.

I followed the steps there to no avail, for in the end I messed up with my graphical mode. I googled like all the afternoon and part of the night, tried other few things, but nothing worked. Finally I reinstalled Kubuntu. Now, after reinstalling, I'm facing the same problem. Everything works fine, but overheats for no reason.

How can I solve this issue, and what causes it? Although I can use the laptop like this, I know that this will greatly shorten my laptop's life, and I think that it is something that should be fixed.

Edit: here is the output of lm-sensors

pch_cannonlake-virtual-0
Adapter: Virtual device
temp1: +50.0°C 

nouveau-pci-0100
Adapter: PCI adapter
temp1: +511.0°C (high = +95.0°C, hyst = +3.0°C)
 (crit = +105.0°C, hyst = +5.0°C)
 (emerg = +135.0°C, hyst = +5.0°C)

iwlwifi-virtual-0
Adapter: Virtual device
temp1: +43.0°C 

coretemp-isa-0000
Adapter: ISA adapter
Package id 0: +46.0°C (high = +100.0°C, crit = +100.0°C)
Core 0: +44.0°C (high = +100.0°C, crit = +100.0°C)
Core 1: +45.0°C (high = +100.0°C, crit = +100.0°C)
Core 2: +45.0°C (high = +100.0°C, crit = +100.0°C)
Core 3: +43.0°C (high = +100.0°C, crit = +100.0°C)

With a temperature of 511ºC, my computer should be melting; since it isn't, it seems that yes, this is drivers-graphics-related

Edit2: When I choose to poweroff, the system crashes and gets stuck, and if I try to close session, there is an error, something like

nouveau E[Xorg[1052]] failed to idle channel 2 [Xorg[1052]]

I managed to solve all the issues by following one simple solution that I found in this post: https://askubuntu.com/questions/1042057/nvidia-drivers-problem-on-kubuntu-18-04

I did not install any NVIDIA drivers, because this was a fresh installation, thus I did not need to remove-purge drivers, so I just run the following two commands in the terminal:

sudo apt-add-repository ppa:graphics-drivers

sudo ubuntu-drivers autoinstall

And it all magically solved after rebooting: lower temperatures, a normal temperature (instead of the 511 crazy degrees), and normal poweroff-rebooting-session closing (however, I needed to perform a hard reboot just after installing the drivers, because the laptop got stuck again with a normal reboot).