Adding a higher resolution mode via xrandr results in a black screen

I'm running Ubuntu 19.10, and I was following the instructions in the answer about how to add a higher resolution mode using xrandr, and I ran into a problem. What I need is to be able to use an external monitor with the 5120 by 2160 resolution. So I first ran cvt:

$ cvt 5120 2160
# 5120x2160 59.99 Hz (CVT) hsync: 134.19 kHz; pclk: 949.00 MHz
Modeline "5120x2160_60.00"  949.00  5120 5536 6096 7072  2160 2163 2173 2237 -hsync +vsync

Having that, I created the mode using xrandr:

$ sudo xrandr --newmode "5120x2160_60.00"  949.00  5120 5536 6096 7072  2160 2163 2173 2237 -hsync +vsync

After that I added the mode to the connected display:

$ sudo xrandr --addmode DP-1-1 "5120x2160_60.00"

It appeared in the output of xrandr:

$ xrandr
Screen 0: minimum 8 x 8, current 3440 x 2592, maximum 32767 x 32767
eDP-1-1 connected 2048x1152+720+1440 (normal left inverted right x axis y axis) 344mm x 194mm
   3840x2160     60.00 +  59.98    59.97  
   ... SNIP ....

DP-1-1 connected primary 3440x1440+0+0 (normal left inverted right x axis y axis) 800mm x 330mm
   3440x1440     59.97*+  59.96    49.99  

   ... SNIP ...

   5120x2160_60.00  59.99    <-- THIS IS THE MODE I NEED
DP-1-2 connected (normal left inverted right x axis y axis)
   2560x2160     59.66  
   640x480       59.94  
DP-1-3 disconnected (normal left inverted right x axis y axis)
  5120x2160_60.00 (0x290) 949.000MHz -HSync +VSync
        h: width  5120 start 5536 end 6096 total 7072 skew    0 clock 134.19KHz
        v: height 2160 start 2163 end 2173 total 2237           clock  59.99Hz

After that I'm trying to switch the monitor to that mode using Ubuntu's settings dialog, but I only get a black screen on the external monitor. What's funny is that I can see the mouse cursor on it, and it moves, but everything else is black, changing the mode back doesn't help - only turning the monitor off and on again gives me the image back. What should I do next?

Here's the output I get from lshw:

$ sudo lshw -C display
  *-display                 
       description: 3D controller
       product: NVIDIA Corporation
       vendor: NVIDIA Corporation
       physical id: 0
       bus info: pci@0000:01:00.0
       version: a1
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress bus_master cap_list rom
       configuration: driver=nvidia latency=0
       resources: irq:182 memory:ec000000-ecffffff memory:c0000000-cfffffff memory:d0000000-d1ffffff ioport:3000(size=128) memory:ed000000-ed07ffff
  *-display
       description: VGA compatible controller
       product: UHD Graphics 630 (Mobile)
       vendor: Intel Corporation
       physical id: 2
       bus info: pci@0000:00:02.0
       version: 00
       width: 64 bits
       clock: 33MHz
       capabilities: pciexpress msi pm vga_controller bus_master cap_list rom
       configuration: driver=i915 latency=0
       resources: irq:151 memory:eb000000-ebffffff memory:80000000-8fffffff ioport:4000(size=64) memory:c0000-dffff