How to install Treble ROM in Redmi 4X(Santoni)

Pre-requisites:-

• Redwolf Recovery(Treble supported)
• Lineage 15.1 (Unofficial) (By Swapnil Soni)
• Magisk 16.4 (If you want to root)
• Download generic system image file from the following  

1. Bootleggers GSI
2. Dirty Unicorn GSI
3. AOSP Extended(AEX) GSI
4. DotOS GSI
5. Resurrection Remix GSI
6. Aquarius OS GSI
7. AOSIP GSI 

You can download this file below and install this with gapps 8.1 ARM64 if you want AEX treble.......

1. AOSPAEX ROM.zip(By Issac Chen) 

Just flash it...
Or use the below method by using generic system image..

Installation:-

1.  First install Redwolf recovery over TWRP ...........
2. Then reboot↻ to Redwolf recovery
3. Then select WIPE and clean every thing except MicroUSB and SDcard
4. Then install Lineage 15.1 and Gapps( ARM64) 
5. Then again reboot ↻ to recovery
6. Then go to WIPE → wipe only system
7. Then go to INSTALL → install the GSI image you have downloaded  ( If you have downloaded .zip file , just extract it)
8. Then again install Gapps and Magisk (if you want to root)
9. Then wipe Dalvik cache and cache
10. Then Reboot↻.................

                         👌That's it👌