Source: https://askubuntu.com/questions/1075157/unable-to-set-my-screen-resolution-higher
Ubuntu or the other versions of it like (k,l,x,edu,etc.,) are required to add the resolution we want to set on some monitors.
So follow my steps:-
Open a Terminal by CTRL+ALT+T
Type xrandr and ENTER
Note the display name usually VGA-1 or HDMI-1 or DP-1
Type cvt 1920 1080 (to get the --newmode args for the next step)
Type sudo xrandr --newmode "1920x1080_60.00" 173.00 1920 2048 2248 2576 1080 1083 1088 1120 -hsync +vsync
Type sudo xrandr --addmode DP-1 "1920x1080_60.00"
and ENTER (replace VGA-1 with your display type (step 3) like HDMI-1 or DP-1)
Now close the terminal and go to Settings >> Display settings and change it to 1920x1080 Enjoy FHD.
To make the above settings stick when you restart your computer, do the following.
For integrated displays
goto your terminal and type vim ~/.profile ENTER
Paste in the shell command from step 5 and 6, then save.
For external displays
create a script called external_monitor_resolution.sh in the directory /etc/profile.d/. using sudo vim /etc/profile.d/external_monitor_resol.sh.
Paste in the shell command from step 5 and 6, then save.
(Note: if using sudo would require you typing a password, your system might freeze on startup while waiting for you to input a password. So when pasting do away with the sudo) Something like this:
xrandr --newmode "1920x1080_60.00" 173.00 1920 2048 2248 2576 1080 1083 1088 1120 -hsync +vsync
xrandr --addmode DP-1 "1920x1080_60.00"`
and ENTER (replace VGA-1 with your display type (step 3) like HDMI-1 or DP-1)