I was facing a very annoying screen flashing/flickering of backlight with Ubuntu 20.04 LTS on Dell XPS laptop. After some searching I found this thread with a user reporting similar issue:

https://bugs.launchpad.net/ubuntu/+source/gnome-settings-daemon/+bug/1827790

Then I edited the grub config file:

$ sudo vi /etc/default/grub

Changing the default parameter to:

GRUB_CMDLINE_LINUX_DEFAULT="i915.enable_psr=0 quiet splash"

And then:

$ sudo update-grub

It didn’t fix the issue completely, but now it is at least more smooth and don’t bother me too much.

Update: Changing the Power settings Automatic Brightness to Off and Dim Screen When Inactive to Off solved the remaining issues.