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. 😃