Hello, I need your help to be able to correctly go to version V5 of the plugin. Here is my configs as a whole.

confi.yml: https://pastebin.com/5v5YkYu4
default.yml: name: default
joueur.yml: https://pastebin.com/TXEVvBt8

Currently I am using the extension you provided. However as you said it is only temporary so I would like your help to make the transition correctly.

Very nice work on this new version! Congratulations !

Just make joueur a parent of default.

I directed you to the actual section:
https://github.com/lucko/LuckPerms/wiki/Default-Groups#configure-inheritance (Note the #configure-inheritance)

Hello, how do you think I do this?

This is explained here: https://github.com/lucko/LuckPerms/wiki/Default-Groups#configure-inheritance