I hate it because it was developed by Israeli spyware company Amdocs in Israel. Then it moved to the UK but on a forum someone who appears to be a dev denies that Amdocs ever did spyware (they wiretapped Bill Clinton and many other scandals)

The main Matrix server is Element, hosted by the developers of Matrix. And the server can see a lot of info not necessarily the messages but a lot of metadata. So unless people use a custom Matrix server it’s actually not private at all