(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)
> If you don't store that data or delete it, you can't provide it.
Can I do this easily and still have my homeserver work correctly with Matrix?
Anyway, the law would probably require any operator to keep this data for a while since they have access to it. And I can't rely on my contact's homeservers to delete this data even if they can (technically and legally).
Now, include lower level technical Details such as the IP layer.
1. Imagine you connect to a server to send a message. Now, you send a message to someone else. The server can't see who you are, right? Because the letter misses your name. Imagine someone else sends a message to you.
2. Imagine you to connect to the same server to receive messages that the server stored for delivery with your name on it. The server gives you the messages.
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)