Hi @Espace Loisirs - I appreciate you putting on your English hat (and also had a past career as a social worker! Those were some long days )
To Troy’s point above, you can't do a two-way sync between apps. That being said, you could set up any number of Zaps to send things one way, depending on what you wish to accomplish.
So when looking here you can see the list of available triggers for a Zap, in this case, SendInBlue:
You could use the “New or Updated Contact” Trigger to then send the information into your Google Contacts. Not as ideal, it sounds, as your desired workflow, but hopefully it would still save you some time that you can better use elsewhere.
Let me know your thoughts, and I’m happy to continue being creative about finding the right solution for you!