Update: MIUI 11 for Mi A2 Lite released on July 2021, Android version is 10. This is the last update for this phone.
Fastboot Flash: To flash firmware using fastboot, the phone’s bootloader must be unlocked.
EDL Flash: Unlocking bootloader is not required to flash firmware using Qualcomm EDL mode. EDL (Qualcomm Emergency Download) mode is useful for unbricking and downgrading.
Downgrade: Sometimes downgrades can block or brick your phone due to the Android Roll Breaking system. If your phone already has ARB protection, there is no possibility to use old version MIUI.