Hey Guys,
To add more, I installed a fresh LibreElec v10.0.0. I installed the add on Raspbery pi tools, System tools and Adafruit Librairies (not sure it helps) from the repos.
I installed the dedicated argon one libreelec script: "curl argonone-setup-libreelec.sh | bash"
It was obviously not working at first.
I only needed to update the "/storage/.config/system.d/argononed.service" and change the ExecStart line with this one : ExecStart=/bin/sh -c ". /etc/profile; exec /usr/bin/python /storage/.config/argononed.py".
Everything then went fine and I was able to manage the fan control through the config file.
Have Fun,
Damien.