There are no update plans for the Mi Mix 3 5G, it has emerged. Contradicting Xiaomi Customer Support, the 5G edition of the Mi Mix 3 is still yet to receive any form of OS upgrade from Android 9.0 Pie or MIUI 10.
https://www.notebookcheck.net/Xiaomi-has-no-update-plans-for-the-Mi-Mix-3-5G.482442.0.html