Secondary monitor not connecting in 18.04 LTS

Found a workaround:

    xrandr --addmode HDMI-1-2 1920x1080
    xrandr --output HDMI-1-2 --mode 1920x1080

This sequence of commands enables clone display. However, I still don't see anywhere in Displays/Monitors the secondary display.

Here is the xrandr output (while projector is on):

    HDMI-1-2 disconnected 1920x1080+0+0 (normal left inverted right x axis y axis) 0mm x 0mm
       1920x1080     60.02* 

I have two graphics cards in my Dell Notebook, Intel and NVidia.
After updating, this problem appeared and I solved it with the following command

sudo prime-select nvidia