I have a laptop with both Integrated Intel and an Nvidia GPU:
Output from lspci:
00:02.0 VGA compatible controller: Intel Corporation HD Graphics 620 (rev 02)
01:00.0 3D controller: NVIDIA Corporation GM108M [GeForce 940MX] (rev a2)
I was messing around trying to get the Nvidia graphics drivers working properly, as you do, because I couldn't open the Nvidia X Server Settings, and there's a weird HDMI screen I can't seem to connect detect (others can), although my HDMI works fine with plenty of other connections. Let's leave that for another question.
Anyway, in the process of changing trying to switch between using the Nvidia and Intel GPUs, my resolution was locked to a possible two values below 1200^2 pixels (can't remember particular numbers).
I tried re-installing default graphics drivers, upgrading from nvidia-390 to nvidia-430 (recommended), reverting back to nvidia-390 and pending that fail decided to upgrade the OS to 19.04. Funnily enough, doing so has actually fixed my Nvidia X Server settings issue, which is sweet, but I'm still locked in resolution, now to a single value 960x540.
The weird bit is that every time I restart my laptop, the login screen is always in full native 1080x1920p, and as soon as I login, the graphics will blank for a sec ( presumably switching server or something) and give me my limited option. Logging out also brings me back to 1080p, but another login back to 960x540.
As I want to detect proper resolutions of connected devices, I'm wondering if there's something I should do rather than manually implement a xrandr --newmode option (which does work btw, I can use this to change the resolution as I've seen a few other answers - here or here).
Output from xrandr:
Screen 0: minimum 8 x 8, current 960 x 540, maximum 16384 x 16384
eDP-1-1 connected primary 960x540+0+0 (normal left inverted right x axis y axis) 309mm x 173mm
960x540 59.82*
864x486 59.92 59.57
640x480 59.94
480x270 59.82
432x243 59.92 59.57
320x240 60.05
HDMI-1-1 disconnected (normal left inverted right x axis y axis)
DP-1-1 disconnected (normal left inverted right x axis y axis)
HDMI-1-2 disconnected (normal left inverted right x axis y axis)
