All users to be members of all groups...

In my purpose, users do not need to join any groups , they should be group s members ''automatically"' to all groups ( or a list of them) and they will have choice to join or not  events within groups....

Maybe an autoaction button to synchronise with the user list ? I do not know how I could implement this (if it is doable)

The "Group Auto Join" fieldtype and the CB GroupJive auto action type do not have functionality for joining all groups only specific groups.

Guess the easiest way to join all groups is to just write a database query for that and is probably the safest option as depending on how many groups you have could be heavy to loop through every single one of them in PHP. It'd have to be an insert select against _groupjive_users that joins _groupjive_groups since group id is needed.

I don't really recommend doing this though and isn't really the intended usage of CB GroupJive as it's meant to be self-managed communities and won't stop those users from just leaving those groups if they wanted.

The "Group Auto Join" fieldtype and the CB GroupJive auto action type do not have functionality for joining all groups only specific groups.

Oh that's OK for me if I can do group per group but I do not know where to find Group Auto Join fieldtype . Is it an action in CB AutoAction ?

It's a fieldtype within CB > Field Management. It lets users select groups to automatically join during registration and/or profile edit. It acts as just a normal field you can place wherever you like during registration and/or profile edit. If you want to just force them into groups without having them select anything you'd need to use CB Auto Actions.