Does nomodeset prevent me to change the screen resolution?

How can I change my screen resolution to 1368x768 on Xubuntu 18.04? I tried jaakko@jaakko-GL553VW:~$ xrandr xrandr: Failed to get size of gamma for output default Screen 0: minimum 1920 x 1080, current 1920 x 1080, maximum 1920 x 1080 default connected 1920x1080+0+0 0mm x 0mm 1920x1080 77.00* Modeline (0x2db) 1368.000MHz h: width 85 start 1368 end 1440 total 1576 skew 0 clock 868.02KHz v: height 1784 start 768 end 771 total 781 clock 1111.42Hz jaakko@jaakko-GL553VW:~$ xrandr --newmode Modeline "1368x768_60.00" 85.25 1368 1440 1576 1784 768 771 781 798 xrandr: Failed to get size of gamma for output default X Error of failed request: BadName (named color or font does not exist) Major opcode of failed request: 140 (RANDR) Minor opcode of failed request: 16 (RRCreateMode) Serial number of failed request: 19 Current serial number in output stream: 19 jaakko@jaakko-GL553VW:~$ Then I type less /etc/default/grub the output is # If you change this file, run 'update-grub' afterwards to update # /boot/grub/grub.cfg. # For full documentation of the options in this file, see: # info -f grub -n 'Simple configuration' GRUB_DEFAULT=0 GRUB_TIMEOUT_STYLE=hidden GRUB_TIMEOUT=0 GRUB_DISTRIBUTOR=lsb_release -i -s 2> /dev/null || echo Debian GRUB_CMDLINE_LINUX_DEFAULT="nomodeset" GRUB_CMDLINE_LINUX="" # Uncomment to enable BadRAM filtering, modify to suit your needs # This works with Linux (no patch required) and with any kernel that obtains # the memory map information from GRUB (GNU Mach, kernel of FreeBSD ...) #GRUB_BADRAM="0x01234567,0xfefefefe,0x89abcdef,0xefefefef" # Uncomment to disable graphical terminal (grub-pc only) #GRUB_TERMINAL=console # The resolution used on graphical terminal # note that you can use only modes which your graphic card supports via VBE # you can see them in real GRUB with the command `vbeinfo' #GRUB_GFXMODE=640x480 # Uncomment if you don't want GRUB to pass "root=UUID=xxx" parameter to Linux #GRUB_DISABLE_LINUX_UUID=true # Uncomment to disable generation of recovery mode menu entries #GRUB_DISABLE_RECOVERY="true" # Uncomment to get a beep at grub start #GRUB_INIT_TUNE="480 440 1"