Today, I debugged a strange x11vnc issue, that results in a strange effect:
when enabling the on-screen-keyboard on my tablet, it paints most areas black.
After messing with a bunch of x11vnc options, I noticed:

Jun 24 12:19:42 desktop bash[3778]: 24/06/2024 12:19:42 Sending
rfbEncodingExtDesktopSize for size (5119x1600)
Jun 24 12:19:42 desktop bash[3778]: 24/06/2024 12:19:42 Client requested
resolution change to (2560x1600)
Jun 24 12:19:43 desktop bash[3778]: 24/06/2024 12:19:43 Sending
rfbEncodingExtDesktopSize for size (5119x1600) resize prohibited

Digging further on my desktop for this issue:

$ xrandr
Screen 0: minimum 8 x 8, current 5119 x 1600, maximum 32767 x 32767
DP-2.8 connected 2560x1600+2559+0 (normal left inverted right x axis y axis)
641mm x 401mm
   2560x1600     59.97*+
   1920x1200     59.88  
   1920x1080     60.00    59.94    50.00    23.98  
   1680x1050     59.95  
   1600x1200     60.00  
   1280x1024     75.02    60.02  
   1280x800      59.81  
   1280x720      60.00    59.94    50.00  
   1152x864      75.00  
   1024x768      75.03    60.00  
   800x600       75.00    60.32  
   720x576       50.00  
   720x480       60.01    59.94  
   640x480       75.00    59.94    59.93  
HDMI-0 disconnected (normal left inverted right x axis y axis)
DP-0 connected primary 2560x1600+0+0 (normal left inverted right x axis y axis)
641mm x 401mm
   2560x1600     59.97*+
   1920x1200     59.88  
   1920x1080     60.00    59.94    50.00    23.98  
   1680x1050     59.95  
   1600x1200     60.00  
   1280x1024     75.02    60.02  
   1280x800      59.81  
   1280x720      60.00    59.94    50.00  
   1152x864      75.00  
   1024x768      75.03    60.00  
   800x600       75.00    60.32  
   720x576       50.00  
   720x480       60.01    59.94  
   640x480       75.00    59.94    59.93  
DP-1 disconnected (normal left inverted right x axis y axis)
DP-2 disconnected (normal left inverted right x axis y axis)
DP-3 disconnected (normal left inverted right x axis y axis)
DP-4 disconnected (normal left inverted right x axis y axis)
DP-5 disconnected (normal left inverted right x axis y axis)

If I add the horizontal numbers for the two monitors, that makes 5120 pixel,
not 5119.

This is a classical off-by-one, but where to start digging?

Checked Xorg GitLab:
https://gitlab.freedesktop.org/xorg/lib/libxrandr
https://gitlab.freedesktop.org/xorg/app/xrandr

libxrandr didn't received any changes after release, which is on par with our
TW release 1.5.4.

xrandr saw some unrelated commits after 1.5.2. I tried to apply
71ab94418ead8f59c6124e8b3e53f8df7340f095 already:

https://build.opensuse.org/package/show/home:frispete:Tumbleweed/xrandr

Did not change anything.