Comment # 1 on bug 1208724 from Marco Calistri

Hello,

It follows how I have resolved my issue.

First of all, add the last parameter to /etc/default grub (in bold):

GRUB_CMDLINE_LINUX_DEFAULT="resume=/dev/disk/by-uuid/4ff65e75-c664-43d8-ab25-25d85336f6b8
mitigations=auto quiet acpi_backlight=native"

Then create the following file: /etc/X11/xorg.conf.d/20-intel.conf with this
content:

Section "Device"
    Identifier  "Intel Graphics"
    Driver      "intel"
    Option      "Backlight"  "intel_backlight"
EndSection


Finally, modify the startup script to adjust the initial brightness level:

echo -n 700 > /sys/class/backlight/intel_backlight/brightness

Now my system starts with the right brightness level (the one I choose) and
resume from suspend also by keeping the same brightness intensity.

Problem solved!

Best regards,