Comment 31 for bug 1870736

Same for me.
Ubuntu 20.04 nvidia-driver-390 (also tried 340.108), GeForce GT-750M

I noticed some weird behavior with the xrandr, note the "mm" size is different for the same scale setting at different times.

greg@LapXPS:~$ xrandr --verbose --output eDP-1-1 --scale 2x2
screen 0: 6400x3600 846x475 mm 192.10dpi
crtc 0: 3200x1800 59.98 +0+0 "eDP-1-1"
greg@LapXPS:~$ xrandr --verbose --output eDP-1-1 --scale 1.25x1.25
crtc 0: disable
screen 0: 4000x2250 527x296 mm 192.51dpi
crtc 0: 3200x1800 59.98 +0+0 "eDP-1-1"
greg@LapXPS:~$ xrandr --verbose --output eDP-1-1 --scale 1.5x1.5
screen 0: 4800x2700 1587x892 mm 76.81dpi
crtc 0: 3200x1800 59.98 +0+0 "eDP-1-1"
greg@LapXPS:~$ xrandr --verbose --output eDP-1-1 --scale 1.25x1.25
crtc 0: disable
screen 0: 4000x2250 1321x743 mm 76.88dpi
crtc 0: 3200x1800 59.98 +0+0 "eDP-1-1"
greg@LapXPS:~$ xrandr --verbose --output eDP-1-1 --scale 1.5x1.5
screen 0: 4800x2700 1587x892 mm 76.81dpi
crtc 0: 3200x1800 59.98 +0+0 "eDP-1-1"
greg@LapXPS:~$ xrandr --verbose --output eDP-1-1 --scale 1.75x1.75
screen 0: 5600x3150 1850x1040 mm 76.88dpi
crtc 0: 3200x1800 59.98 +0+0 "eDP-1-1"
greg@LapXPS:~$ xrandr --verbose --output eDP-1-1 --scale 2x2
screen 0: 6400x3600 2113x1188 mm 76.93dpi
crtc 0: 3200x1800 59.98 +0+0 "eDP-1-1"
greg@LapXPS:~$ xrandr --verbose --output eDP-1-1 --scale 1x1
crtc 0: disable
screen 0: 3200x1800 1056x594 mm 76.97dpi
crtc 0: 3200x1800 59.98 +0+0 "eDP-1-1"
greg@LapXPS:~$ xrandr --verbose --output eDP-1-1 --scale 1.75x1.75
screen 0: 5600x3150 1480x832 mm 96.05dpi
crtc 0: 3200x1800 59.98 +0+0 "eDP-1-1"
greg@LapXPS:~$ xrandr --verbose --output eDP-1-1 --scale 1.75x1.75
screen 0: 5600x3150 1480x832 mm 96.05dpi
crtc 0: 3200x1800 59.98 +0+0 "eDP-1-1"
greg@LapXPS:~$ xrandr --verbose --output eDP-1-1 --scale 1x1
crtc 0: disable
screen 0: 3200x1800 845x475 mm 96.17dpi
crtc 0: 3200x1800 59.98 +0+0 "eDP-1-1"
greg@LapXPS:~$ xrandr --verbose --output eDP-1-1 --scale 1.25x1.25
screen 0: 4000x2250 528x297 mm 192.10dpi
crtc 0: 3200x1800 59.98 +0+0 "eDP-1-1"
greg@LapXPS:~$ xrandr --verbose --output eDP-1-1 --scale 1x1
crtc 0: disable
screen 0: 3200x1800 422x237 mm 192.42dpi
crtc 0: 3200x1800 59.98 +0+0 "eDP-1-1"
greg@LapXPS:~$ xrandr --verbose --output eDP-1-1 --scale 1.75x1.75
screen 0: 5600x3150 740x416 mm 192.10dpi
crtc 0: 3200x1800 59.98 +0+0 "eDP-1-1"