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WhatsApp provides no cryptographic management for group messages
(arstechnica.com)
This is a most excellent place for technology news and articles.
If you want your group memberships to be known only by the group members, use Signal.
Just use signal is not a valid statement in a world where vast majority of people aren't using (and won't use) it. I have been trying to get people to install it and have a total of 6 over several years. They only use it to communicate with me.