Alright, since Canonical ltd (Due to legal reasons) cannot do anything with NVIDIA’s Proprietary Driver including technical supports or bug reports about NVIDIA problems on Ubuntu Discourse. Unfortunately Ubuntu’s NVIDIA Additional Driver has limitations on a fan speed by default, which means if you install a GPU driver with sudo ubuntu-drivers autoinstall to install a recommended version you have an APT version of NVIDIA Settings and NVIDIA SMI that will cause limitations and will not let us to change a fan what we need to, luckily I have found a workaround that should solve that issue to get fan control to work functionally, this step by steps will fix that.
Here’s a step by steps
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Download a driver that matches with your driver version from NVIDIA website when looking at
nvidia-smion a terminal ornvidia-settings --version, because some reason the NVIDIA X Settings app and NVIDIA SMI both are using an old driver version like 510 or older while your driver is up-to-date which causes compatibility issues like fan speed will remain automatic and cannot be changed, maybe is something have to do with an APT version of these guys. Because using an APT version does have an out of date apps which causes functionality issues. -
Run this command on a terminal
sudo /home/*USERNAME*/downloads/NVIDIA-Linux-x86_64-*VERSION*.run --no-kernel-module --no-nvidia-modprobe --no-x-check --no-cc-version-check -a
Reminder:
The use of these guys --no-kernel-module --no-nvidia-modprobe --no-x-check --no-cc-version-check -a is to install an unmodulated driver, which we need that along side with Ubuntu’s NVIDIA driver to do a workaround. 
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Select NVIDIA proprietary in a setup and install 32-bit compatibility by select yes.
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If its asking for X configuration update, hit yes (This shouldn’t hurt you Linux Device) and reboot (Optional but recommended just in case).
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After you’re able to boot to Linux, run
sudo nvidia-settingson a terminal and change your fan speed if you want (Please note the rebooting will reset the fan speed) -
To make NVIDIA X Settings in root mode and make it permanent, copy and paste this and save it as
nvidia-settings.desktopin“/home/“username”/.local/share/applications”partition.
Like this.
[Desktop Entry]
Type=Application
Encoding=UTF-8
Name=NVIDIA X Server Settings
Comment=Configure NVIDIA X Server Settings
Exec=gnome-terminal -e "sudo /usr/bin/nvidia-settings"
Icon=nvidia-settings
Categories=Settings;HardwareSettings;
# Translation by Marcin Mikołajczak
Name[pl]=Ustawienia serwera X NVIDIA
Comment[pl]=Narzędzie konfiguracyjne dla ustawień serwera X NVIDIA
# Translation by RDL
Name[ru]=Параметры NVIDIA X Server
Comment[ru]=Конфигурирование параметров NVIDIA X Server
# Translation by Tractix
Name[ro]=Setări NVIDIA X Server
Comment[ro]=Configurează setările NVIDIA X Server
[/details]
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Save and exit before run it and it should pop up a terminal with a administrator password required before launching NVIDIA X Settings in a Sudo/Root Mode and then you should be good to go on changing a fan speed if you want. Because running NVIDIA X Settings in normal mode won’t let you change a fan speed until running it in sudo mode.
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Alternatively: Perhaps you could just instead make a file to change a fan speed entirely with two options and it’s much easier.
For GPU with 2 fans
sudo nvidia-settings -a “[gpu:0]/GPUFanControlState=1”
sudo nvidia-settings -a “[fan:0]/GPUTargetFanSpeed=100”
For GPU with 3 fans
sudo nvidia-settings -a “[gpu:0]/GPUFanControlState=1”
sudo nvidia-settings -a “[fan:0]/GPUTargetFanSpeed=100”
sudo nvidia-settings -a “[fan:1]/GPUTargetFanSpeed=100”
Please note that the changes of the fan speed will be reset on a reboot, so you’re going have to repeat a step 8 if you want a full fan speed. Also aware that if you update Ubuntu’s NVIDIA driver, make sure you start over this workarounds or else fan speed may be not working. But I really wish there’s a way for laptop users and palmtop users to have a fan speed changes on Linux with nvidia-settings.
To uninstall an unmodulated Proprietary driver:
Type sudo nvidia-uninstall and hit yes to uninstall it, if that failed type sudo ubuntu-drivers autoinstall to restore an APT version if that works.
Reminder:
Fan Speed Control only works on a desktops (Not Laptops nor Palmtops), perhaps if you wanna see your RTX GPU fan speed, use Hardware sensor indicator by installing this to get started and see your RTX GPU on a Top-bar.
sudo apt install indicator-sensors
when play games on Ubuntu, this workaround is for everyone that are Ubuntu or its flavors.
. I’ve done it myself, it worked like a 
JAM 
.