Brightness button click responses are very slow on Ubuntu 18.04 LTS

I have ASUS X550LD Recently I installed Ubuntu 18.04 LTS which comes with GNOME, later I moved to KDE Plasma. KDE details are in below screenshots:

I also installed nvidia driver using below commad:

sudo apt install nvidia-driver-390

Graphics driver related details:

thelittlenaruto@thelittlenaruto-X550LD:~$ sudo lshw -C display
  *-display                 
       description: VGA compatible controller
       product: Haswell-ULT Integrated Graphics Controller
       vendor: Intel Corporation
       physical id: 2
       bus info: pci@0000:00:02.0
       version: 09
       width: 64 bits
       clock: 33MHz
       capabilities: msi pm vga_controller bus_master cap_list rom
       configuration: driver=i915 latency=0
       resources: irq:50 memory:f7400000-f77fffff memory:d0000000-dfffffff ioport:f000(size=64) memory:c0000-dffff
  *-display
       description: 3D controller
       product: GF117M [GeForce 610M/710M/810M/820M / GT 620M/625M/630M/720M]
       vendor: NVIDIA Corporation
       physical id: 0
       bus info: pci@0000:04:00.0
       version: a1
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress bus_master cap_list rom
       configuration: driver=nvidia latency=0
       resources: irq:52 memory:f6000000-f6ffffff memory:e0000000-efffffff memory:f0000000-f1ffffff ioport:d000(size=128) memory:f7000000-f707ffff
thelittlenaruto@thelittlenaruto-X550LD:~$ 

Here is a snippet of /etc/default/grub :

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="quiet splash acpi_backlight=video nvidia-drm.modeset=1"
GRUB_CMDLINE_LINUX=""

Afterall these, my brightness button responds very late like 4-5 minutes. Meaning it doesn't reflect the brightness changes immediately. Any solution?

Output of journalctl -xe :

thelittlenaruto@thelittlenaruto-X550LD:~$ journalctl -xe
May 02 05:30:58 thelittlenaruto-X550LD systemd[1]: This usually indicates unclean termination of a previous ru
May 02 05:30:58 thelittlenaruto-X550LD systemd[1]: Started Tool to automatically collect and submit kernel cra
-- Subject: Unit kerneloops.service has finished start-up
-- Defined-By: systemd
-- Support: http://www.ubuntu.com/support
-- 
-- Unit kerneloops.service has finished starting up.
-- 
-- The start-up result is RESULT.
May 02 05:30:58 thelittlenaruto-X550LD whoopsie[1235]: [05:30:58] Using lock path: /var/lock/whoopsie/lock
May 02 05:30:58 thelittlenaruto-X550LD nm-dispatcher[1049]: req:5 'connectivity-change': new request (1 script
May 02 05:30:59 thelittlenaruto-X550LD nm-dispatcher[1049]: req:4 'dhcp4-change' [wlp3s0]: start running order
May 02 05:30:59 thelittlenaruto-X550LD nm-dispatcher[1049]: req:5 'connectivity-change': start running ordered
May 02 05:31:00 thelittlenaruto-X550LD whoopsie[1235]: [05:31:00] offline
May 02 05:31:00 thelittlenaruto-X550LD systemd[1]: Started Message of the Day.
-- Subject: Unit motd-news.service has finished start-up
-- Defined-By: systemd
-- Support: http://www.ubuntu.com/support
-- 
-- Unit motd-news.service has finished starting up.
-- 
-- The start-up result is RESULT.
lines 2340-2361/2361 (END)