External monitor through 'HDMI - USB-C adapter' detected, but gives black screen

I’ve recently bought a new Asus TUF Gaming A15 laptop which has a HDMI and a USB-c port. My setup is as follows:

Laptop: Asus TUF Gaming A15
OS: Kubuntu 20.04
Monitor 1: Laptop screen
Monitor 2: Connected through HDMI
Monitor 3: Connected with a HDMI in a HDMI to USB-C connector in the USB-C port of the laptop

Now the strange thing is that the second monitor on the USB-c is detected, but gives a black screen. It doesn’t matter whether monitor 2 is connected or not, it is always the same result. The xrandr output is:

    Screen 0: minimum 320 x 200, current 6400 x 1440, maximum 16384 x 16384
eDP connected 1920x1080+0+0 (normal left inverted right x axis y axis) 344mm x 194mm
 1920x1080     59.98*+
 1680x1050     59.98   
 1280x1024     59.98   
 1440x900      59.98   
 1280x800      59.98   
 1280x720      59.98   
 1024x768      59.98   
 800x600       59.98   
 640x480       59.98   
HDMI-A-0 connected primary 2560x1440+1920+0 (normal left inverted right x axis y axis) 7
25mm x 428mm
 2560x1440     59.95*+  74.97   
 1920x1200     59.95   
 1920x1080     60.00    50.00    59.94   
 1600x1200     59.95   
 1280x1440     59.91   
 1680x1050     59.88   
 1280x1024     75.02    60.02   
 1440x900      59.90   
 1280x960      60.00   
 1280x800      59.95   
 1280x720      60.00    50.00    59.94   
 1024x768      75.03    70.07    60.00   
 832x624       74.55   
 800x600       72.19    75.00    60.32    56.25   
 720x576       50.00   
 720x480       60.00    59.94   
 640x480       75.00    72.81    66.67    60.00    59.94   
 720x400       70.08   
DP-1-0 connected 1920x1080+4480+0 550mm x 340mm panning 1920x1440+4480+0 tracking 6400x1
440+0+0 border 0/0/0/0
 1920x1200     59.95 +
 1920x1080     59.94*   59.93    50.00   
 1680x1050     59.95   
 1600x1200     60.00   
 1440x900      74.98    59.89   
 1280x1024     75.02    60.02   
 1280x720      60.00    59.94   
 1152x864      75.00   
 1024x768      75.03    70.07    60.00   
 800x600       75.00    72.19    60.32   
 720x576       50.00   
 720x480       59.94   
 640x480       75.00    72.81    59.93    59.94   
DP-1-1 disconnected
1920x1080 (0x63) 148.500MHz +HSync +VSync
      h: width  1920 start 2448 end 2492 total 2640 skew    0 clock  56.25KHz
      v: height 1080 start 1084 end 1089 total 1125           clock  50.00Hz
1280x1024 (0x68) 135.000MHz +HSync +VSync
      h: width  1280 start 1296 end 1440 total 1688 skew    0 clock  79.98KHz
      v: height 1024 start 1025 end 1028 total 1066           clock  75.02Hz
1280x1024 (0x69) 108.000MHz +HSync +VSync
      h: width  1280 start 1328 end 1440 total 1688 skew    0 clock  63.98KHz
      v: height 1024 start 1025 end 1028 total 1066           clock  60.02Hz
1280x720 (0x6d) 74.250MHz +HSync +VSync
      h: width  1280 start 1390 end 1430 total 1650 skew    0 clock  45.00KHz
      v: height  720 start  725 end  730 total  750           clock  60.00Hz
1024x768 (0x70) 78.750MHz +HSync +VSync
      h: width  1024 start 1040 end 1136 total 1312 skew    0 clock  60.02KHz
      v: height  768 start  769 end  772 total  800           clock  75.03Hz
1024x768 (0x71) 75.000MHz -HSync -VSync
      h: width  1024 start 1048 end 1184 total 1328 skew    0 clock  56.48KHz
      v: height  768 start  771 end  777 total  806           clock  70.07Hz
1024x768 (0x72) 65.000MHz -HSync -VSync
      h: width  1024 start 1048 end 1184 total 1344 skew    0 clock  48.36KHz
      v: height  768 start  771 end  777 total  806           clock  60.00Hz
800x600 (0x75) 49.500MHz +HSync +VSync
      h: width   800 start  816 end  896 total 1056 skew    0 clock  46.88KHz
      v: height  600 start  601 end  604 total  625           clock  75.00Hz
800x600 (0x74) 50.000MHz +HSync +VSync
      h: width   800 start  856 end  976 total 1040 skew    0 clock  48.08KHz
      v: height  600 start  637 end  643 total  666           clock  72.19Hz
800x600 (0x76) 40.000MHz +HSync +VSync
      h: width   800 start  840 end  968 total 1056 skew    0 clock  37.88KHz
      v: height  600 start  601 end  605 total  628           clock  60.32Hz
720x576 (0x78) 27.000MHz -HSync -VSync
      h: width   720 start  732 end  796 total  864 skew    0 clock  31.25KHz
      v: height  576 start  581 end  586 total  625           clock  50.00Hz
720x480 (0x7a) 27.000MHz -HSync -VSync
      h: width   720 start  736 end  798 total  858 skew    0 clock  31.47KHz
      v: height  480 start  489 end  495 total  525           clock  59.94Hz
640x480 (0x7b) 31.500MHz -HSync -VSync
      h: width   640 start  656 end  720 total  840 skew    0 clock  37.50KHz
      v: height  480 start  481 end  484 total  500           clock  75.00Hz
640x480 (0x7f) 25.175MHz -HSync -VSync
      h: width   640 start  656 end  752 total  800 skew    0 clock  31.47KHz
      v: height  480 start  490 end  492 total  525           clock  59.94Hz

This is a screenshot of the Display Configuration:

All looks good, but the screen just shows a black screen. Whenever I change the resolution of that monitor, for example, it makes these noises it should make when changing the resolution. So something is working. Also the monitor says it gets input, only the input is entirely black. The information page on the monitor itself shows:

Also

• In Windows 10 the monitor works fine through the hdmi to usb-c connector, so it is a specific linux problem
• When I switch my two external monitors, it gives the same result: the monitor connected through HDMI directly works, the monitor connected through USB-C doesn’t work
• I’ve tried several HDMI to USB-C connects, all give the same result
• I’ve tried another distro, Manjaro KDE, gives the same result
• I’ve tried the Nvidia Proprietary drivers 450 and this week updated to the most recent, 455. Both drivers give the same result

What could be the problem? Would be nice in these Corona-times to have 3 working monitors on my Linux installation. Many thanks for your help in advance.