Android 10 on the Mi Mix 3 has been a long time coming, with Xiaomi first releasing a beta build for the device way back in October. While the company issued Android 10 for Chinese handsets in January, the rest of the world has had to wait patiently. Thankfully, that wait is over and the 2.0 GB update should now be arriving as an OTA.
https://www.notebookcheck.net/The-Mi-Mix-3-finally-receives-Android-10-globally-its-first-OS-upgrade.456002.0.html