[Redmi K20 Pro / Xiaomi Mi 9T Pro ROMs, Kernels, Re] kingkong1981:
Sharing my cleanflash experience;

I recommend cleanflash over dirty flash for unofficial versions of any custom ROM, though painful but worth the effort.

Official version of lineage OS ROM can update through OTA using their official recovery though.

Safeguard your current data;

Sync all your accounts in settings so that contacts etc. important data can be restored later online.

Contacts can also be exported to a VCF file and saved, to be imported later.

Use a USB type C cable to transfer important data from internal storage (explore all folders) of your phone to your PC.

Take a complete NANDroid backup image of phone through TWRP Recovery or Titanium Backup of apps, that can be restored later if any of following steps go wrong.

Unlock Bootloader;

In Phone;

Requires a working internet connection (mobile data)

In Mi Account login using email id & password linked to phone number (very important)

Xiaomi Cloud> turn on Find Device & sync xiaomi cloud

Settings> About Phone> Tap MIUI version several times to enable Developer options in Additional settings

Turn on USB debugging, OEM unlocking & Mi Unlock status in Developer Options

In Mi Unlock status> Add account & device

i.mi.com > login using same email id & password linked to phone number (imp) & locate your device

Boot k20 pro into fastboot by pressing volume down & power buttons simultaneusly from power off state and connect it to pc using USB type C cable.

In PC;

login using same email id & password linked to phone number (imp) in your latest version of mi unlock tool using internet connection and in settings click the button to install the driver.

Unlock successfully

Cleanflash steps;

Remove pin, password, pattern lock, finger print, face lock & all account passowords to avoid getting locked into your own device.

Enable USB debugging in Developer settings of your phone and authorize your device.

Developer settings can be enabled by tapping on build number in settings several times.

Install minimal ADB & fastboot & phone USB drivers to your PC.

Connect your PC to your phone (in power off mode) using USB type C cable.

Boot your phone into boot loader (fastboot) by pressing and holding together power & volume down buttons till an android cartoon appears on phone display.

Install twrp-3.5.0_9-0-raphael.img (official version of twrp recovery for Redmi K20 Pro/ Mi 9T Pro) by the following command in minimal ADB & fastboot interface of your PC;

fastboot flash recovery twrp-3.5.0_9-0-raphael.img

Reboot into the installed recovery by pressing and holding together power & volume up buttons till the home screen of recovery appears.

Use Recovery to,

Wipe> Advanced Wipe> wipe partitions - Dalvik/ ART Cache, Cache, System, Data & Internal Storage except Vendor

Factory Reset

Flash following files in order through Advanced > ADB Sideload or OTG stoarge drives;

RAPHAELININGlobal-V12.0.3.0.QFKINXM-10.0-vendor-firmware.zip (is Indian Firmware, but for other regions kindly choose correct firmware)

lineage-18.1-20210222-UNOFFICIAL-raphael.zip (latest ROM)

NikGapps-core-arm64-11-20210130-signed.zip (basic Google Apps with playstore functionality)

Magisk-v21.4.zip (for banking/ payment apps to function properly)

Reboot> System

Hope, I was of some help