The Snapdragon 855-powered Mi Mix 3 5G was launched about a year ago. Since then, it hasn't received a major OS update, and remains stuck on Android Pie with no hope for a change of status ianytime soon. Even worse, the Mi Mix 3 5G hasn't gotten the MIUI 11 update either, and owners of the phone refuse to take that sitting down.
https://www.notebookcheck.net/Mi-Mix-3-5G-owners-take-up-arms-in-response-to-Android-10-and-MIUI-11-snub.464420.0.html