The Xiaomi Mi Mix 2S was one of the few devices to be a part of Google’s Android Pie Beta program, so it was bound to get a stable version of Pie well before any other Xiaomi devices. Other devices from the company had to do with Global Beta updates to Android Pie. You can now download Android Pie based on MIUI 10 for the Xiaomi Mi Mix 2S.
The Xiaomi Mi Mix 2S is a successor of the original Xiaomi Mi Mix which debuted the world's first selfie camera that was on the bottom chin of the phone. The device came with top-of-the-line hardware for the time and did fairly well, despite Xiaomi's odd design choices. The Xiaomi Mi Mix 3 is around the corner and is expected to be released later this year, based on a teaser posted on Weibo by the company's president and co-founder. It appears to feature a sliding camera like the Oppo Find X but does away with the automatic sliding mechanism.
Android Pie for Xiaomi Mi Mix 2S not available OTA just yet
The MIUI Global Beta based on Android Pie comes in the form of a recovery ROM, so you’ll have to manually sideload it, which requires a custom recovery like TWRP. You don't have to wipe the device before attempting the upgrade, but we recommend that you do. Installing the update shouldn’t wipe your data, unlocking your bootloader certainly will. MIUI 10 also has its new features as well as all the bells and whistles of Android Pie including a newly redesigned Recents menu, AI-powered pre-loading of apps, and the proved camera capabilities. Here's how you go about it. Go ahead with the process only if you absolutely cannot wait for Android Pie. There should be an OTA around the corner, hopefully. After all, there is a stable version of Pie online already.
News Source: XDA developers