@sebastian-roth
No problem regarding my disappointment. I am especially sorry that I didn’t succeed like a great one 
I know many open source projects and I contribute to some of them: PeerTube, OpenStreetMap. I’m very happy to have discovered Fog and to have been able to quickly clone posts and 1 classe. I work in a French school with limited IT resources.
So, to answer your question, I followed a tutorial from the forum.
I started to disable apparmor on my container with :
Edit the container configuration file and add the line lxc.aa_profile: unconfined.
On Proxmox the configuration file is located at /etc/pve/lxc/CTID.conf, where CTID is the ID number of the container.
and I restarted container and the script but not better.
Then I did step 2 of this page: https://wiki.fogproject.org/wiki/index.php?title=Installation#LXC but no better.
I also tried to enable NFS in the options. Anyway, I think I did everything but I wonder if I did some things wrong.
So, what do you advise me for FOG on Proxmox 6.3-2? Maybe I’ll have to start from scratch… and focus on one action, but which one? and how do you know if the NFS server is running without having to restart the script?
Thanks for your help!