I want to use three screens with my Ubuntu 21.04 laptop.
My hardware:
- Laptop: Dell Precision 5510
 
- Dock: Dell Dock WD19 (2x DisplayPort, 1x HDMI)
 
- Screen 1: DELL P2719H -> Connected via DisplayPort
 
- Screen 2: Dell UP2716D -> Connected via DisplayPort -> capable of 2560 x 1440, but I only use 1920 x 1080 because the other is limited to 1920 x 1080 and the monitors only work at the same resolution (which is okay for me)
 
I updated to Ubuntu 21.04 today an promptly ran into the issue that my two external screens are recognized but remain dark. I can configure all three screens (the laptop screen being the third) but the laptop screen is the only one working. I can move windows to the other two screens but as said, they remain black. Both screens say there is "No DP signal from your device".
xrandr says:
Screen 0: minimum 8 x 8, current 5760 x 1080, maximum 16384 x 16384
eDP-1-1 connected primary 1920x1080+3840+0 (normal left inverted right x axis y axis) 346mm x 194mm
   1920x1080     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  
   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-1-1 disconnected (normal left inverted right x axis y axis)
HDMI-1-1 disconnected (normal left inverted right x axis y axis)
DP-1-2 disconnected (normal left inverted right x axis y axis)
HDMI-1-2 disconnected (normal left inverted right x axis y axis)
DP-1-1-1 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 598mm x 336mm
   1920x1080     60.00*+
   1600x900      60.00  
   1280x1024     75.02    60.02  
   1152x864      75.00  
   1024x768      75.03    60.00  
   800x600       75.00    60.32  
   640x480       75.00    59.94  
   720x400       70.08  
DP-1-1-2 disconnected (normal left inverted right x axis y axis)
DP-1-1-2-8 connected 1920x1080+1920+0 (normal left inverted right x axis y axis) 597mm x 336mm
   2560x1440     59.95 +
   2048x1080     60.00    24.00  
   1920x1080     60.00*   50.00    59.94  
   1600x1200     60.00  
   1280x1024     75.02    60.02  
   1152x864      75.00  
   1280x720      60.00    50.00    59.94  
   1024x768      75.03    60.00  
   800x600       75.00    60.32  
   720x576       50.00  
   720x480       60.00    59.94  
   640x480       75.00    60.00    59.94  
   720x400       70.08  
DP-1-1-2-1 disconnected (normal left inverted right x axis y axis)
DP-1-1-3 disconnected (normal left inverted right x axis y axis)
Maybe there is an issue with "*+" not being at the same resolution for the last display?
I've been thinking to buy a third screen and keep my laptop lid closed for some time now. I want to buy the DELL P2719H (= Screen 1) again and use three external screens. This problem made me consider this option even harder now.
Now my question is: Can I run three external monitors with my setup? And can I run the two DELL P2719H  (= Screen 1 and the new one) via DisplayPort and Dell UP2716D (= Screen 2) via HDMI at the same time? Or is it not possible to to combine HDMI and DisplayPort?
If not possible, would it work when I daisy-chain tow screens? Connect Screen 1 and Screen 2 to my Dock and chain the new Screen 3 to Screen 2?
Ideally I'd like to have Screen 1 and the new Screen 3 in landscape orientation and Screen 2 in portrait.
If nothing works, maybe someone has at least an idea how I can fix my two screens from going dark? That way I'd be stuck with two external screens and my laptop screen, but at least I can use three screens again. With my Ubuntu 20.04 setup (before updating to 21.04) two external screens and the laptop screen worked. So I don't think it is a hardware issue.
WIth 21.04 I selected "NVIDIA driver metapackage from nvidia-driver-460 (proprietary, tested)" in "Software & Updates -> Additional Drivers". I also tried "NVIDIA driver metapackage from nvidia-driver-465 (proprietary)" with the same result.