system uses intel UHD620 graphics i5 8250 + bumblebee nvidia 130mx

refresh rate of monitor is always set on lowest value in system settings ->
display and monitor. which is 48hz.

glxgears confirms it. 


glxgears
Running synchronized to the vertical refresh.  The framerate should be
approximately the same as the monitor refresh rate.
243 frames in 5.0 seconds = 48.436 FPS
240 frames in 5.0 seconds = 47.998 FPS
240 frames in 5.0 seconds = 47.999 FPS

but xrand shows correct value:
 xrandr
Screen 0: minimum 8 x 8, current 1920 x 1080, maximum 32767 x 32767
eDP1 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis)
340mm x 190mm
   1920x1080     60.00*+  59.93    48.00  
   1680x1050     59.88  
   1400x1050     59.98  
   1600x900      60.00    59.95    59.82  
   1280x1024     60.02  
   1400x900      59.96    59.88  
   1280x960      60.00  
   1368x768      60.00    59.88    59.85  
   1280x800      59.81    59.91  
   1280x720      59.86    60.00    59.74  
   1024x768      60.00  
   1024x576      60.00    59.90    59.82  
   960x540       60.00    59.63    59.82  
   800x600       60.32    56.25  
   864x486       60.00    59.92    59.57  
   640x480       59.94  
   720x405       59.51    60.00    58.99  
   640x360       59.84    59.32    60.00  
HDMI1 disconnected (normal left inverted right x axis y axis)
VIRTUAL1 disconnected (normal left inverted right x axis y axis)


similar problem I found in arch forums:
https://bbs.archlinux.org/viewtopic.php?id=232354

setting by hand to 59.93 gives this result:

glxgears
Running synchronized to the vertical refresh.  The framerate should be
approximately the same as the monitor refresh rate.
305 frames in 5.0 seconds = 60.886 FPS
298 frames in 5.0 seconds = 59.593 FPS
300 frames in 5.0 seconds = 59.997 FPS