XDA contributors claim to have found references to code-names for 4 different new Xiaomi phones in this OEM's software. There is also evidence that all of these devices will have the state-of-the-art 108MP Samsung image sensor that should inform the apex of smartphone cameras going into 2020. Furthermore, it is possible that the Mi Mix 4 is not one of them.
https://www.notebookcheck.net/Xiaomi-may-have-as-many-as-4-108MP-camera-phones-in-the-works-for-2020-already.434064.0.html