Xiaomi has no update plans for the Mi Mix 3 5G
The Mi Mix 3 5G is something of an outcast among Xiaomi smartphones. Released in May 2019, the device is more than just a Mi Mix 3 with a 5G modem. Xiaomi also equipped it with a larger battery and a new chipset, almost making it a Mi Mix 3.5.
Having more powerful components does not correlate with better software support, though. On the contrary, the Mi Mix 3 5G is still without an OS upgrade since launching on Android 9.0 Pie. Worse still, the Mi Mix 3 5G remains on MIUI 10 and has not received an update in any region since Xiaomi issued V10.3.23.0.PEMEUXM to EU devices in February.
Xiaomi Customer Support had informed at least one person that the device would receive MIUI 12 in October 2020, although still based on Android 9.0 Pie. However, that may not necessarily be the case. According to an announcement on Mi Community about a new update for the regular Mi Mix 3, "there is no update plans [sic] for the 5G variant". An update may still arrive at some point, but there is no fixed time for when it will be released.