Can see the following under settings. But I have not changed anything in the BIOS. Then again, it is not a Thunderbolt port that is in the Asus PN50. There is a USB-c port for data transfer, DisplayPort functionality. See more here: https://www.asus.com/Mini-PCs/Mini-PC-PN50/
Ah, so Gnome Desktop.
Have you disabled Secure Boot in your BIOS?
Have you installed Gnome-tweak tool?
sudo apt-get install gnome-tweaks
What does
xrandr -q
Show you? Does it list all devices?
Does your configuration file contain any content?
sudo nano /etc/X11/xorg.conf.d/10-monitor.conf
You may be able to change screen resolution through terminal with the xrandr --addmode command, but that will not address why only one display is being detected.
Try
lspci -tv
To chjeck devices.
You can install with (I think. I am not on Gnome Desktop)
sudo apt install bolt
You may need to upgrade your kernel if you need to install bolt. What kernel are you running, now?
uname -a
gnome-tweaks has been installed now 
xrandr -q
-sigh-
Failed to get size of gamma...
Can I go bang my head against the wall,now?
If you do not have it yet:
sudo apt-get install inxi
Then paste output of
inxi -G
kernel 5.4
morten@morten-MINIPC-PN50:~$ inxi -G
Graphics: Card: Advanced Micro Devices [AMD/ATI] Device 1636
Display Server: x11 (X.Org 1.20.8 )
drivers: fbdev,ati (unloaded: modesetting,vesa,radeon)
Resolution: 1280x1024@77.00hz
OpenGL: renderer: llvmpipe (LLVM 10.0.0, 128 bits)
version: 3.3 Mesa 20.0.8
morten@morten-MINIPC-PN50:~$
Not much concern, there. Mesa and OpenGL version looks a bit low to me, but shouldn't not work.
I am sorry to do this to you, but can you pose the output of
sudo lshw
Would usb-c to hdmi cable resolve the issue plus some xrandr tweaking?
Community Moderator
Maybe. Will buy a display cable tomorrow. Then one with HDMI and one with display port. So should one be able to use 2 screens on Zorin os?
I am using two screens now. I was using three, until one of the monitors power card went out.
Okay that sounds good. Then I just do it, instead. From what I have been able to read, there is something about the Linux kernel itself. That they do not support usb-c monitors 100 percent
Can you please reference a link to that? I just tried a search on it and only found some slightly old threads mentioning it. The Linux kernel is up to 5.8 or so, now.
It is possible that information is outdated.
And yes, upping your kernel to 5.6 May help. I admit, I am running 5.5.0-5550 for no other reason than to test it. I figured that was risky on my main machine, but I have had no problems with it.
The above article might be helpful.
Have seen many websites through about that problem. So can not remember any particular pages. But the ones I find it were a bit old (1-2 years old)
Yes it could be very interesting. But do not quite understand how to do it?
Hi now I have bought a display cable. So now I have 2 monitors set to computer one with HDMI and the other with display port. One now it can not see the screen with HDMI? What do I need to do to make it work with 2 screens? I am running on Zorin OS 15.3 with latest update
In terminal, let's try
sudo dpkg-reconfigure gdm
Select GDM3
Reboot.
If no change, then in terminal,
sudo nano /lib/systemd/system/gdm3.service
Find this line:
ExecStartPre=/usr/share/gdm/generate-config
Replace it with this one:
ExecStartPre=/usr/bin/xinit /usr/share/gdm/generate-config
In terminal,
sudo nano /etc/X11/Xwrapper.config
Add the following line, then exit and save as original title
needs_root_rights=yes
If still no good, try:
sudo apt install intel-gpu-tools
intel-virtual-output
Reboot