The app leaks your IP address to the server by default. Roughly 50% of your contacts will use same server cloud provider (Akamai or Flux) as you, and that company can end-to-end correlate your conversations with that contact. Always use SimpleX with Tor if you actually want to get rid of user identifiers.
I’d argue the apps that hide your IP by default and that use no (de)centralized servers provide better privacy: Cwtch, Quiet, Ricochet Refresh, OnionShare chats, and Briar.