1. Make sure your A20 is rooted (https://forum.xda-developers.com/sho...95&postcount=4
2. Backup with Titanium Backup (optional)
3. Install TWRP
4. Backup boot, data & system onto external SD or usb-otg. If something goes wrong you should be able to restore the phone using TWRP.
5. Installing GSI from TWRP.
a. Download the desired GSI (it MUST be A/B_arm64 Variant)
-One GSI can be found in post #1
b. unpack it if it wasn't in .IMG format
c. Go to TWRP , Install , Install IMAGE
d. Pick your GSI and select SYSTEM IMAGE and go to wipe, advanced, wipe both caches
e. Reboot. If that doesn't work reboot to TWRP Recovery and flash "GSI_Fix_boot.zip"
Ignore the message that says can't mount storage
f. Reboot system. If that doesn't work reboot to TWRP and wipe data. Then reboot system.
Enter all data.
Reboot into TWRP and backup boot, data & system
You may need to flash Magisk zip to get root.
This worked for me