Fix the blur with picom

uninstall picom

The blur is avalaible only for the git version,
So if you have it from pacman you have to remove it.

sudo pacman -R picom

Install picom

This is the git:
https://aur.archlinux.org/packages/picom-git/

git clone https://aur.archlinux.org/picom-git.git
cd picon-git
makepkg -si

Start it with i3

I have to add experimental-backends in my config.
.config/i3/config

exec --no-startup-id picom -b --experimental-backends

Picom conf

I have nothing to add on it but you can modify things like you want.
.config/picom/picom.conf