Recently, a developer on XDA developer’s forum posted a beta unofficially to a variety of Qualcomm Snapdragon Treble-enabled devices. Boot up the Android P for Mi A1 device. The unofficial port of Android P has been released for the Xiaomi Mi A1. Although, the device doesn’t actually support Project Treble so you have to “Trebelize” it first, as the developer says.
The initial build had quite a bit of issues like a broken fingerprint scanner, camera, and Bluetooth. On the release of a newer version of ROM, The only major issue right now is that VoLTE doesn’t work and SELinux set to permissive. Keep in mind that installing the custom ROM requires re-partitioning your device, which will require you to erase your phone, so keep the backups!
The flashing instructions are quite long and detailed, so make sure to follow every step carefully.
The full detailed information here