The problem with this machine is that it only outputs 1920p to a 4K monitor with Ubuntu, which is pretty annoying. According to the Dell Inspiron 13-5379 spec the connector is HDMI 1.4a, which should support 4K. However, only HDMI 2.0 supports 4K with 60FPS, HDMI 1.4a only supports 4K with 25 or 30 FPS. My Inspiron employs Intel i7-8550U which should support 4K at 60FPS.

In order to add support for 4k resolution, a new modeline needs to be added. I’ve found this awesome modeline generator. The modeline generated for 30 FPS didn’t work, but the 25 FPS worked. In order to add the modeline and switch to it, run the following in the terminal:

xrandr --newmode "3840x2160_25.00" 278.70 3840 4056 4464 5088 2160 2161 2164 2191 -HSync +Vsync
xrandr --addmode HDMI-1 "3840x2160_25.00"
xrandr --output HDMI-1 --mode "3840x2160_25.00"

Note that the above only works when Ubuntu is running on Xorg. Trying the above while running on Wayland, on the XWAYLAND1 output fails in the last step:

$ xrandr --output XWAYLAND1 --mode "3840x2160_25.00"
xrandr: Configure crtc 0 failed

The controls are rather tiny with the default scale of 100%. You can open the Gnome “Displays” configuration and selecting the 200% upscale, to restore the proper sizes. The general problem with 4K resolutions is that Gnome loses its speed and the entire desktop starts behaving “choppy” which is quite annoying.