When plugging in and unplugging the ac the brightness goes to 100%

inxi -Fxxz
  Kernel: 5.15.57-2-MANJARO arch: x86_64 bits: 64 compiler: gcc v: 12.1.0
    Desktop: i3 v: 4.20.1 dm: LightDM Distro: Manjaro Linux base: Arch Linux
  Type: Laptop System: LENOVO product: 20L6S1LV2F v: ThinkPad T480
    serial: <superuser required> Chassis: type: 10 serial: <superuser required>
  Mobo: LENOVO model: 20L6S1LV2F v: SDK0J40697 WIN
    serial: <superuser required> UEFI: LENOVO v: N24ET69W (1.44 )
    date: 05/25/2022
  ID-1: BAT0 charge: 6.5 Wh (35.1%) condition: 18.5/23.9 Wh (77.4%)
    volts: 11.2 min: 11.4 model: LGC 01AV489 serial: <filter>
    status: not charging
  ID-2: BAT1 charge: 9.4 Wh (45.4%) condition: 20.7/24.0 Wh (86.2%)
    volts: 11.3 min: 11.5 model: SMP 01AV452 serial: <filter>
    status: discharging
  Info: quad core model: Intel Core i5-8350U bits: 64 type: MT MCP
    arch: Coffee Lake rev: A cache: L1: 256 KiB L2: 1024 KiB L3: 6 MiB
  Speed (MHz): avg: 800 min/max: 400/1901 boost: disabled cores: 1: 800
    2: 800 3: 800 4: 800 5: 800 6: 800 7: 800 8: 800 bogomips: 30409
  Flags: avx avx2 ht lm nx pae sse sse2 sse3 sse4_1 sse4_2 ssse3 vmx
  Device-1: Intel UHD Graphics 620 vendor: Lenovo driver: i915 v: kernel
    arch: Gen-9.5 ports: active: eDP-1 empty: DP-1, DP-2, HDMI-A-1, HDMI-A-2
    bus-ID: 00:02.0 chip-ID: 8086:5917
  Device-2: Chicony Integrated Camera (1280x720@30) type: USB
    driver: uvcvideo bus-ID: 1-8:2 chip-ID: 04f2:b604
  Display: x11 server: X.Org v: 21.1.4 compositor: Picom v: git-7e568
    driver: X: loaded: intel gpu: i915 display-ID: :0 screens: 1
  Screen-1: 0 s-res: 1920x1080 s-dpi: 96
  Monitor-1: eDP-1 mapped: eDP1 model: LG Display 0x0521 res: 1920x1080
    dpi: 157 diag: 355mm (14")
  OpenGL: renderer: Mesa Intel UHD Graphics 620 (KBL GT2) v: 4.6 Mesa
    22.1.4 direct render: Yes
  Device-1: Intel Sunrise Point-LP HD Audio vendor: Lenovo ThinkPad T480
    driver: snd_hda_intel v: kernel bus-ID: 00:1f.3 chip-ID: 8086:9d71
  Sound Server-1: ALSA v: k5.15.57-2-MANJARO running: yes
  Sound Server-2: JACK v: 1.9.21 running: no
  Sound Server-3: PulseAudio v: 16.1 running: yes
  Sound Server-4: PipeWire v: 0.3.56 running: yes
  Device-1: Intel Wireless 8265 / 8275 driver: iwlwifi v: kernel pcie:
    speed: 2.5 GT/s lanes: 1 bus-ID: 03:00.0 chip-ID: 8086:24fd
  IF: wlp3s0 state: up mac: <filter>
  Local Storage: total: 238.47 GiB used: 80.53 GiB (33.8%)
  ID-1: /dev/nvme0n1 vendor: Intel model: SSDPEKKF256G8L size: 238.47 GiB
    speed: 31.6 Gb/s lanes: 4 serial: <filter> temp: 34.9 C
  ID-1: / size: 116.5 GiB used: 80.51 GiB (69.1%) fs: ext4
    dev: /dev/nvme0n1p5
  ID-2: /boot/efi size: 96 MiB used: 25.3 MiB (26.3%) fs: vfat
    dev: /dev/nvme0n1p1
  ID-1: swap-1 type: file size: 8 GiB used: 57.8 MiB (0.7%) priority: -2
    file: /swapfile
  System Temperatures: cpu: 43.0 C pch: 39.5 C mobo: N/A
  Fan Speeds (RPM): fan-1: 0
  Processes: 258 Uptime: 1d 2h 44m Memory: 7.51 GiB used: 2.76 GiB (36.7%)
  Init: systemd v: 251 default: graphical Compilers: gcc: 12.1.0
  clang: 14.0.6 Packages: pacman: 1428 Shell: Bash v: 5.1.16
  running-in: kitty inxi: 3.3.20

GRUB_CMDLINE_LINUX_DEFAULT="quiet udev.log_priority=3 intel_pstate=disable acpi_backlight=vendor"

Maybe i have an xserver stuff that i dont know about? I had problems with my “xstuffs” always, but maybe again?

I read the same exact thread yesterday. You didn’t even try to search, did you?

I only found this acpi_backlight=vendor stuff.

Configure your power settings, somewhere.

I have no de.
Only using a wm. So no power management.

Okay, so the solution was:

Edit /etc/default/grub
instead of

use (in my case) acpi_backlight=intel, then update-grub and then reboot

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