I've been using a dock for my laptop for some time now and it has always worked fine, but now my laptop screen stays black, with the secondary dock monitor working just fine. I have a dual boot with Windows and on there the screen works just fine. With nomodeset the laptop screen does turn on, but then the secondary monitor doesn't work.
I'm running Ubuntu 20.04 on the HP EliteBook 840 G5 3JX27EA. My laptop has Intel graphics. Not sure what info is relevant here but I'd be happy to provide anything else.
Output of xrandr without nomodeset:
Screen 0: minimum 320 x 200, current 3840 x 1412, maximum 16384 x 16384
eDP-1 connected 1920x1080+1920+332 (normal left inverted right x axis y axis) 309mm x 174mm
1920x1080 60.02*+ 60.01 59.97 59.96 59.93 40.00
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
1440x810 60.00 59.97
1368x768 59.88 59.85
1360x768 59.80 59.96
1280x800 59.99 59.97 59.81 59.91
1152x864 60.00
1280x720 60.00 59.99 59.86 59.74
1024x768 60.04 60.00
960x720 60.00
928x696 60.05
896x672 60.01
1024x576 59.95 59.96 59.90 59.82
960x600 59.93 60.00
960x540 59.96 59.99 59.63 59.82
800x600 60.00 60.32 56.25
840x525 60.01 59.88
864x486 59.92 59.57
800x512 60.17
700x525 59.98
800x450 59.95 59.82
640x512 60.02
720x450 59.89
700x450 59.96 59.88
640x480 60.00 59.94
720x405 59.51 58.99
684x384 59.88 59.85
680x384 59.80 59.96
640x400 59.88 59.98
576x432 60.06
640x360 59.86 59.83 59.84 59.32
512x384 60.00
512x288 60.00 59.92
480x270 59.63 59.82
400x300 60.32 56.34
432x243 59.92 59.57
320x240 60.05
360x202 59.51 59.13
320x180 59.84 59.32
DP-1 disconnected (normal left inverted right x axis y axis)
HDMI-1 disconnected (normal left inverted right x axis y axis)
DP-2 disconnected (normal left inverted right x axis y axis)
HDMI-2 disconnected (normal left inverted right x axis y axis)
DP-2-1 connected primary 1920x1200+0+0 (normal left inverted right x axis y axis) 519mm x 324mm
1920x1200 59.95*+
1600x1200 60.00
1680x1050 59.88
1280x1024 60.02
1280x960 60.00
1280x720 60.00
1024x768 60.00
800x600 60.32
640x480 59.94
720x400 70.08
DP-2-2 disconnected (normal left inverted right x axis y axis)
DP-2-3 disconnected (normal left inverted right x axis y axis)
Output with nomodeset:
xrandr: Failed to get size of gamma for output default
Screen 0: minimum 1920 x 1080, current 1920 x 1080, maximum 1920 x 1080
default connected primary 1920x1080+0+0 0mm x 0mm
1920x1080 77.00*
