IMPORTANT: You must flash vbmeta or your phone will fail to boot (until you restore stock recovery):
fastboot flash vbmeta vbmeta.img
I'm very sorry that I forgot to include this instruction initially. If anyone's phone has failed to boot, you can either flash vbmeta and use my TWRP, or flash the stock recovery without flashing vbmeta.
As is mandatory with GPL software, the source code can be found on the GitHub repo redmi8a/android_device_xiaomi_olivelite.
Copyright (c) 2019 Milan Kragujević and contributors. Licensed under GPL 3.0, available here. You are allowed to copy and create derivative works of this content if you preserve the Copyright notice and license it under GPL, while providing the code.
GPL Notice: This work contains code published by Xiaomi and Qualcomm under the GPL v2.0 license, available here. This work is based upon the TWRP project licensed under GPL v3.0, available here.
To learn more about TWRP, visit the official website.
This project is not sponsored, approved or endorsed by Xiaomi, Google, Qualcomm, or TWRP.
Kernel binary distribution NOTICE: In accordance with Section 3c of GPL v2, I am distributing the device kernel in binary form with a forwarded written notice of copyright and source code distribution from Xiaomi. The kernel is being distributed under the terms of the GPL v2 license by Xiaomi and the claimed source code is available here: https://github.com/MiCode/Xiaomi_Ker...ee/olive-p-oss
c) Accompany it with the information you received as to the offer to distribute corresponding source code. (This alternative is allowed only for noncommercial distribution and only if you received the program in object code or executable form with such an offer, in accord with Subsection b above.)
For GPL compliance in case of the precompiled redistributed kernel contact the manufacturer at their official website mi.com.