How to set a higher resolution for 2 external monitors?

Question

I have 2 external monitors that support a resolution up to 3440x1440 (and a laptop screen of 1920x1080) and a Lenovo ThinkPad Thunderbolt 3 Dock Gen 2. While having one external active monitor at 3440x1440 and the laptop screen works, I cannot use both screens at the same time at its maximal resulution. The best setup I can achieve at the moment is the following:

$ xrandr
Screen 0: minimum 320 x 200, current 4480 x 2160, maximum 16384 x 16384
eDP-1 connected primary 1920x1080+1576+1080 (normal left inverted right x axis y axis) 309mm x 173mm
   1920x1080     60.01*+  59.97    59.96    59.93  
   1680x1050     59.95    59.88  
   1600x1024     60.17  
   1400x1050     59.98  
   1600x900      59.99    59.94    59.95    59.82  
   1280x1024     60.02  
   1440x900      59.89  
   1400x900      59.96    59.88  
   1280x960      60.00   
   ...
DP-2-1 connected 2560x1080+0+0 (normal left inverted right x axis y axis) 797mm x 333mm
   3440x1440     49.99 +  59.97  
   2560x1440     59.95  
   2560x1080     60.00*   59.94  
   1920x1080     60.00    50.00    59.94  
   1680x1050     59.88  
   1600x900      60.00  
   1280x1024     75.02    60.02  
   1440x900      59.90  
   1280x800      59.91  
   ...
DP-6 connected 1920x1080+2560+0 (normal left inverted right x axis y axis) 797mm x 333mm
   3440x1440     59.97 +  49.99  
   2560x1440     59.95  
   2560x1080     60.00    59.94  
   1920x1080     60.00*   50.00    59.94  
   1680x1050     59.95  
   1600x900      60.00  
   1280x1024     75.02    60.02  
   1440x900      59.89  
   1280x800      59.81  
   ...

I cannot set a higher resolution for either of the two monitors. For example, when trying to set 2560x1080 for DP-6 I get the following error:

$ xrandr --verbose --output DP-6 --mode 2560x1080
screen 0: 5120x2160 1355x572 mm  95.92dpi
crtc 1:    2560x1080  60.00 +2560+0 "DP-6"
xrandr: Configure crtc 1 failed
crtc 0: disable
crtc 1: disable
crtc 2: disable
screen 0: revert
crtc 0: revert
crtc 1: revert
crtc 2: revert

The following does not work either: 2x 3440x1440, 2x 2560x1440, 2x 2560x1080. Even when turning the laptop monitor off and only having both external monitors, none of these higher resolution setups works. The best I could achieve is the setup shown in the xrandr output above. But that kinda destroys the purpose of one of the ultra wide screens, being stuck at a stretched 1920x1080 (while the second monitor being at 2560x1080 is OK). Why can't I set any higher resolution? I wished to have at least both at a 21:9 resolution of 2560x1080. Any ideas how to achieve that?

My setup:

Laptop: Lenovo T480
OS: Ubuntu 18.04.4 LTS
Kernel: 5.3.0-40-generic
Graphics Card: Intel Corporation UHD Graphics 620
Monitor Connections: HDMI or DP

Answer 1

According to the specs of Intel Corporation UHD Graphics 620 [1], it should be able to support up to 3 monitors up to 4096x2304@60Hz. However, the limiting factor seems to be the docking station. According to the compatibility matrix of the Lenovo ThinkPad Thunderbolt 3 Dock Gen 2 [2] it only supports 2 or 3 monitors (built-in monitor + 2 external monitors) at a maximum resolution of 3840x2160 if used at 30Hz. Unfortunately, I was not able to set both my screens to 3440x1440@30Hz but only one and the other on 2560x1080@30Hz which is okay. Still wondering though why it does not work with both on maximum resolution... Nevertheless, I'm fine with both on a reasonable 21:9 resolution for now. I used the following commands, in case someone else experiences the same issue with external monitors at 60 Hz on a higher resolution and wants to also try it out on 30 Hz:

$ cvt 2560 1080 30
# 2560x1080 29.97 Hz (CVT) hsync: 33.03 kHz; pclk: 106.75 MHz
Modeline "2560x1080_30.00"  106.75  2560 2640 2896 3232  1080 1083 1093 1102 -hsync +vsync

$ cvt 3440 1440 30
# 3440x1440 29.95 Hz (CVT) hsync: 43.96 kHz; pclk: 196.25 MHz
Modeline "3440x1440_30.00"  196.25  3440 3600 3952 4464  1440 1443 1453 1468 -hsync +vsync

# Take values from the cvt commands above
xrandr --newmode "2560x1080_30.00"  106.75  2560 2640 2896 3232  1080 1083 1093 1102 -hsync +vsync
xrandr --newmode "3440x1440_30.00"  196.25  3440 3600 3952 4464  1440 1443 1453 1468 -hsync +vsync

# Use for $1 and $2 whatever xrandr returned, like DP-2 etc.
xrandr --addmode $1 "2560x1080_30.00"
xrandr --addmode $2 "3440x1440_30.00"

xrandr --verbose --output $1 --mode "2560x1080_30.00"
xrandr --verbose --output $2 --mode "3440x1440_30.00"

[1] https://www.intel.com/content/www/us/en/support/products/126789/graphics-drivers/graphics-for-8th-generation-intel-processors/intel-uhd-graphics-620.html

[2] https://support.lenovo.com/in/en/solutions/pd029622