Xposed has a history of not working on MIUI and requiring separate, community-made flashable zip files to function. It works on MIUI 7.9.21+ deodexed ROMs!
This just highlights the work that has to go into making Xposed functional on Android devices. Even when Xposed works, there are still so many variants of Android that the developer needs to account for. The developer behind the port has tested it on the Xiaomi Mi Note 2 running MIUI 9 based on Android Nougat. To install it, simply flash the zip like any other version of Android to use it.
Depending on if you are on Android 7.0 or Android 7.1, you will need to download a different zip file. This is likely because of the changes between Android versions and the changes that had to be made to let Xposed work with MIUI in the first place. The Xposed installer apk is also linked, as it is used also for managing installed modules.
may not work for example, and Xposed even specifically mentions not to use it on anything but AOSP. There are also still some incompatibilities with devices and the port it seems, but still, you should try it and see if it works! There’s a huge amount of modules out there, and if you get the unofficial Xposed working that’s a lot of potential fun to be had.