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