I have a Veon TV that I use as a display for the bedroom pc and its major problem is that it is detected as a resolution of 1920×1080 but its native resolution is actually 1360×768.
With other computers the instructions I dug up were to use xrandr commands in some of the lightdm config settings so this command would be run each time the computer started. I actually did try that this time around (scaling down from a virtual screen of 1920×1080 to a physical of 1360×768) but couldn’t get it to work reliably.
After some more digging I found out how to permanently add the display settings as a modeline. You can make a modeline using the cvt command and then use xrandr –addmode to add this then you can switch to it for testing. For a permanent change you just need to add something like the below to /etc/X11/xorg.conf file:
Section “Monitor”
Identifier “DP-1”
Modeline “1360x768_60.00” 84.75 1360 1432 1568 1776 768 771 781 798 -hsync +vsync
Option “PreferredMode” “1360x768_60.00”
EndSection
Identifier “DP-1”
Modeline “1360x768_60.00” 84.75 1360 1432 1568 1776 768 771 781 798 -hsync +vsync
Option “PreferredMode” “1360x768_60.00”
EndSection
So there you also have your modeline for the correct display. DP-1 in this case is the display output name, which presumably is derived from DisplayPort, but is actually an HDMI output on this computer.
Once that was all set up I was able to force the screen to 1360×768 its native resolution and it has stayed there ever since. Thus bringing an end to horrible 1920×1080 being scaled which made everything on screen too small.