What resolution and frequency does your monitor have? You will probably need to add new modeline.

    pomon My monitor is a 3440 x 1440 (21:9) at 99.98 Hz. Not sure what a new modeline is, but I'll look it up!

        Bhibb My monitor is a 3440 x 1440 (21:9) at 99.98 Hz

        Welcome to the bleeding edge!

          pomon
          3440x1440 98.93 Hz (CVT) hsync: 151.06 kHz; pclk: 720.25 MHz

          Modeline "3440x1440_99.00" 720.25 3440 3728 4104 4768 1440 1443 1453 1527 -hsync +vsync

            try:

            xrandr --newmode Modeline "3440x1440_99.00" 720.25 3440 3728 4104 4768 1440 1443 1453 1527 -hsync +vsync
xrandr  --addmode DisplayPort-0 3440x1440_99.00
xrandr --output DisplayPort-0 --mode  3440x1440_99.00 # or do not perform this command, just go to the monitor settings and see if the monitor is visible

            The monitor should be connected to DisplayPort 0

              pomon When I try this, xrandr doesn't recognize -hsync. I checked the --help and saw that there are valid flags that look like this, but they're not in the right place, probably.

              xrandr: unrecognized option '-hsync'
Try 'xrandr --help' for more information.

                  Bhibb Remove from the first entry Modeline/
                  xrandr --newmode "3440x1440_99.00" 720.25 3440 3728 4104 4768 1440 1443 1453 1527 -hsync +vsyn

                      pomon Perfect, that made the first command work. Your second for adding couldn't find DisplayPort-0

                      xrandr: cannot find output "DisplayPort-0"

                        You've sure you connected the monitor to DisplayPort-0? Xrandr you have:

                        DisplayPort-0 disconnected (normal left inverted right x axis y axis)
                        DisplayPort-1 disconnected (normal left inverted right x axis y axis)

                        Check the port DisplayPort-1

                          pomon Ahh, looks like the naming is a little different here:

                          Screen 0: minimum 8 x 8, current 5360 x 1440, maximum 16384 x 16384
DVI-I-0 disconnected (normal left inverted right x axis y axis)
DVI-I-1 disconnected (normal left inverted right x axis y axis)
HDMI-0 disconnected (normal left inverted right x axis y axis)
DP-0 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 477mm x 268mm
   1920x1080    144.00*+ 144.00   119.93    60.00  
   1600x900     119.95    60.00  
   1280x1024     75.02  
   1280x720      60.00  
   1024x768      75.03    60.00  
   800x600       60.32  
   640x480       59.94  
DP-1 disconnected (normal left inverted right x axis y axis)
DP-2 disconnected (normal left inverted right x axis y axis)
DP-3 disconnected (normal left inverted right x axis y axis)
DP-4 connected primary 3440x1440+1920+0 (normal left inverted right x axis y axis) 797mm x 333mm
   3440x1440     59.97 +  99.98*   49.99  
   2560x1440     59.95  
   2560x1080     60.00    59.94  
   1920x1080     60.00    59.94    50.00  
   1680x1050     59.95  
   1600x900      60.00  
   1440x900      59.89  
   1280x1024     75.02    60.02  
   1280x800      59.81  
   1280x720      60.00    59.94    50.00  
   1152x864      75.00  
   1024x768      75.03    70.07    60.00  
   800x600       75.00    72.19    60.32    56.25  
   720x576       50.00  
   720x480       59.94  
   640x480       75.00    72.81    59.94  
DP-5 disconnected (normal left inverted right x axis y axis)
  3440x1440_99.00 (0x26d) 720.250MHz -HSync
        h: width  3440 start 3728 end 4104 total 4768 skew    0 clock 151.06KHz
        v: height 1440 start 1443 end 1453 total 1527           clock  98.93Hz

                              pomon The monitor looks to be DP-4, currently.

                                Then change DisplayPort-0 to DP-4

                                  pomon When I do that I get another error:

                                  xrandr --addmode DP-4 3440x1440_99.00
X Error of failed request:  BadMatch (invalid parameter attributes)
  Major opcode of failed request:  140 (RANDR)
  Minor opcode of failed request:  18 (RRAddOutputMode)
  Serial number of failed request:  47
  Current serial number in output stream:  48

                                    pomon It just occured to me that maybe you are trying to help the OP instead of me? My monitor is visible to my Solus install and it works. Are we trying to fix the intermittent issue of it sometimes going black?

                                      This error is probably a high frequency of refreshment. Try again without serving the frequency.
                                      cvt 3440 1440

                                        pomon This is the response:

                                        cvt 3440 1440
# 3440x1440 59.94 Hz (CVT) hsync: 89.48 kHz; pclk: 419.50 MHz
Modeline "3440x1440_60.00"  419.50  3440 3696 4064 4688  1440 1443 1453 1493 -hsync +vsync

                                          Well, my mistake. I refer to the entry of the thread founder. 😃