(edit: answering to your initial message, that said that Signal operators also have access to the same metadata, but I guess my comment still answers your sentence "Most important is who when with who which both leak to the server operators" - Signal operators have showed they can't provide this information)
https://signal.org/blog/looking-back-as-the-world-moves-forw...
(edit: answering to your initial message, that said that Signal operators also have access to the same metadata, but I guess my comment still answers your sentence "Most important is who when with who which both leak to the server operators" - Signal operators have showed they can't provide this information)