Brightness always at 100% after reboot

The brightness level of my Asus Vivobook M3500Q (OLED display) gets set to 100% brightness after every reboot.
I tried to automatically run a script on startup with the command

brightnessctl -d "amdgpu_bl0" set 30%

This doesn't work without sudo. With sudo, it cannot run in the background as it asks for the password.
What else can I do? Maybe somebody can find the reason of my notebook forgetting the last brightness setting instead of helping the to set the brightness to a pre-defined level on every startup?