When I did below operation it could show the full desktop.
For 3840 x 2160 $ xrandr --output DP-5 --scale 2x2
For 7680 x 4320 $ xrandr --output DP-5 --scale 4x4
When I did below operation it could show the full desktop.
For 3840 x 2160
$ xrandr --output DP-5 --scale 2x2
For 7680 x 4320
$ xrandr --output DP-5 --scale 4x4