[Redmi K20 Pro / Xiaomi Mi 9T Pro Guides, News, & D] Sandeeep Kiran:
**** Disclaimer: I'm not responsible if you destroy your device. Learn at your own risk!!! ****

Alright, So I am a bit Moderately skilled to Custom Development. I do not know a lot of in-depth either.

However, I do know enough to help other new beginners out.

As I continue to learn more info and details, I will update this post frequently.

Completed guide, I'm saving and typing as not to lose progress. Last Updated- 01/03/2021

Please do note, CROSS-VERIFY if the info here is correct before following it.

What is a Custom ROM?

Simply put, it is a new Operating System [OS].

People find their stock (the one you got with your phone) to be boring, or they dislike it or want more customization and optimization, lesser bloatware (useless unwanted system apps).

Thus some Developers made their own ROM (aka OS). Then others made it compatible with our phone. Sometimes this works perfectly, most of the time it doesn't. Thus Asking people how the ROM is, is always good to ask.

How To Get a Custom ROM?

So, to flash (insert) a new Custom ROM, we first need to unlock the Bootloader. The Bootloader is what allows us to wipe (remove/erase) our data, and current OS and flash a different one.

Then we flash a Recovery. (A software that makes flashing and wiping and other stuff easy)

Then flash the ROM, Then (if needed) vendor+firmware, gapps, magisk.

How To Unlock Bootloader?

So, you should first update your software to the latest miui OS [current: MIUI 11].

Go to Settings > About Phone > tap on MIUI Version 7 times -> you unlock developer settings

Go to Settings > Additional Settings > Developer Options > enable (switch on) USB Debugging > OEM Unlocking > click on MI Unlock status > link account and device.

To link the account, you must first have a Xiaomi MI account. You can make this in settings, or head to https://account.xiaomi.com

Wait 7-15 days

Once 7-15 days have passed,

USING WINDOWS PC

BACKUP ALL FILES, CONTACTS, WHATSAPP, ANY APP settings (if any), AND SYNC/LINK accounts to cloud => YOU WILL LOSE EVERYTHING NOW

Now download the Mi Unlock tool onto your PC https://xiaomitools.com/mi-unlock-tool-en/

IN A SEPERATE FOLDER

Then download Platform Tools from attachments below.

Then download TWRP (team win recovery project) from https://dl.twrp.me/raphael/

Then download Orange Fox Recovery (OFRP) from https://files.orangefox.tech/OrangeFox-Stable/raphael/ and download the latest file. [Currently: OrangeFox-R-10.1_3-Stable-raphael.zip]

Then download Disable force encrypt zip file from attachments below

Then download adb drivers from https://www.xda-developers.com/what-is-adb/ version 1.4.3 onto your PC and run the application. (Follow from How do I install ADB?) (Or you can skip that and just get the file from attachments below and extract it to C drive as a separate folder directly)

Then download the ROM (links are given below)

Then download gapps (optional). from https://opengapps.org/ and select ARMx64 and PICO then the download button.

Then download Magisk (optional). from https://github.com/topjohnwu/Magisk/releases download the Latest Magisk-vXX.xx.zip file there.[Currently: Magisk-v20.4.zip]

Download the latest vendor file from the below links. (make sure it's the proper file for your device's variant.)

Vendor and firmware are both combined and included in the same zip file.

Global, EEA (Europe), China, Russia Q Vendor: https://xiaomifirmwareupdater.com/archive/vendor/raphael/

Indian Q Vendor: https://xiaomifirmwareupdater.com/archive/vendor/raphaelin/

Check my third comment to learn how to recognize which device variant is yours, and what vendor to download and flash.

NOW! GET READY!

Now, connect your device.

Use your cable included in the box (the charging wire) and connect it to your phone and PC.

Go to 'adb' folder in your C-drive, (on that address bar thing where it shows) This PC >OS(C:)> adb click on it and type cmd . This will open a Command prompt to that folder.

Type adb devices and on your phone tap on the authorize button that pops up when unlocked. Now type adb devices again.

you will get

List of devices attached
365278234e device

Now, Switch off your phone.

Open the MI Unlock Tool on your PC, run the file that is an application. Read through everything, click on unlock, confirm.

Wait till the phone fully reboots itself.

DON'T TOUCH IT NOW!

Congrats, the phone is now unlocked, and you have stock MIUI 11.

Now skip everything in the setup (we wanna add a custom ROM now remember, why stop here?)

again do the adb devices. You should get the same results.

Now, on your PC

Extract the Platform Tools zip file so you get its folder.

Move the TWRP.img file into the folder.

Open that folder. on that address bar, type cmd to get a new command prompt window.

There type dir *img to confirm the file is found properly.

Now switch off your phone again.

press and hold the power button + volume down button.

you will soon enter fastboot mode.

Now, on the new command prompt where you typed dir *img

type fastboot devices and you will get an output like

342524356 fastboot

Then type fastboot flash recovery twrp(press the TAB key to autofill)

Now it's done! you have TWRP, but it isn't permanent.

Now, TWRP usage.

Now press and hold power key + volume up to enter TWRP.

Once in TWRP, unlock it.

Go to MOUNT and check if MTP is enabled..... click on "enable MTP" button.

Now copy the ofox.zip (orange fox recovery zip file) to your phone from your PC via your PC.

Now go to INSTALL tap the ofox.zip file, then flash it!

YAY now, orangefox is your Permanent Recovery.

Now go to MENU > Manage Partitions > select only data > format data

Now go to MENU > Reboot > Recovery

Now, to Flash your first Custom Rom.

Now from your PC copy the ROM zip file, Disable decrypt zip file, gapps ( if specified, optional), magisk ( if you want to root, optional)

Now go to MENU > Reboot > Recovery

Now go to FILES > tap on the ROM zip > add to queue > tap disable decrypt zip file > add to queue > (add gapps , magisk if needed) > flash

Now wait for a while (approx 10mins) till ROM boots up and complete the setup process.

Congrats you have your new ROM.

Now just let google download all your apps

Before you change settings like dark mode or use custom launchers etc...

Reboot once for the heck of it. Then Customize the way you like.

**** Backup Your Persist and save it on your PC always. ****

How To Change My ROM? I wanna Try them all!

Now is the easy part, since all the setup is done!

First remove all passwords, fingerprints, and so forth.

For AOSP ROMs: (MIUI below)

AOSP ROMs will not break your L1

First Download the AOSP ROM you want, given below are some examples. (MIUI below)

Each of these might have instructions, usually saying...

Go to your Recovery, (press and hold Power + Volume Up buttons).

Then go to WIPE > select Dalvik, Cache, System, Data > then wipe them all.

Then go to [Files in OFX] [Install in TWRP] and

Only If you are coming from miui and flashing AOSP, go to orangefox settings > manage partitions > data > format > type yes (you lose everything in internal storage) then

Select the Vendor (if it's needed) (not required if moving between any android 10 ROMs) (Just make sure it's the right Vendor for your device/region) (If the previous AOSP rom uses OSS vendor, then you need to wipe vendor as well and flash the stock before proceeding) and flash it.

Select the ROM (Then > add to queue, else if you only needed ROM, just flash. and set-up! yay!)

DFE (not required if you want to be encrypted, which is not recommended.) (A must if you formatted data via orangefox settings and did that typing 'yes' thing)

Gapps (if it isn't already included in the ROM, ask first).

and Magisk (optional if you want root).

For MIUI ROMs: (AOSP above)

First Download the MIUI based ROM you want ( stock, EU, MortalOS, etc), given below are some examples.

Each of these might have instructions, usually saying...

Go to your Recovery, (press and hold Power + Volume Up buttons).

Select the Vendor (if it's needed) (not required if it's currently the proper Vendor, cause EU ROMs to use a custom vendor that works on all devices) (Just make sure it's the right Vendor for your device/region) and flash it.

Then go to WIPE > select Dalvik, Cache, System, Data, Vendor > then wipe them all. (make sure you are on your device's vendor region before wiping it.)

Then go to [Files in OFX] [Install in TWRP] and

Only If you are coming from AOSP and flashing MIUI, go to orangefox settings > manage partitions > data > format > type yes (you lose everything in internal storage) then

Select the ROM (Then > add to queue, else if you only needed ROM, just flash. and set-up! yay!)

DFE (A must if you formatted data via orangefox settings and did that typing 'yes' thing)

Magisk (optional if you want root).

Some Android ROMs

With ROMs being built, changed, and modified on a daily/weekly basis. Some changing to Mi9 fod or LOS fod or using Stock or OSS vendors. Sometimes maintainers shifting or 2 devs building the same rom. The below list is not being maintained anymore. We currently have 50 ROMs. YAY Raphael!

Update: I'm removing most of the ROMs listed here and only adding my personal favorite ROMs

AOSP ROMs

DerpfestOS (two variants, I like em both) - by @Raaj52 -> https://xdaforums.com/k20-pro/development/rom-derpfest-t4132757

SuperiorOS by @HSgod -> https://xdaforums.com/k20-pro/development/rom-superioros-t4130867

MortalOS (miui12) by @Raaj52 -> https://xdaforums.com/k20-pro/development/rom-havoc-os-3-3-t4063081

LineageOS, Pixel Experience, PE+, PE+ Fan Edition, ParanoidOS, MookeOS, TitaniumOS, MSM Xtended, OxygenOS, OmniOS, TreskMod, AOSIP, ColtOS, ArrowOS, BootleggersOS, ExtendedUI (exui), CRdroidOS, RevengeOS, IonOS, AICP, BlissOS, CorvusOS, DerpfestOS, HavocOS, NitrogenOS, HentaiOS, Corvus, TitianiumOS, CygnusOS, CesiumOS, Project 404, DescendantOS, SyberiaOS, EvolutionX, AOSPA, POSP, LegionOS, AncientOS, RebellionOS, SuperiorOS, ShapeshiftOS, WrathOS, ZenX, AIM OS, ConquerOS, PixelDustOS, CygnusOS, StagOS, Ressurection Remix OS, Quartz, PixysOS, PePlusUI, MalluOS, StatixOS, GrapheneOS, ShapeshiftOS, MortalOS, SuperiorOS, AwakenOS, DotOS, Lemon Branch, FluidOS, LiquidOS + more!

MIUI ROMs

EU ROMs, MortalOS, RevolutionOS, Miroom, MMX, Masik + 5 other ROMs

Kernels

Perf (miui kernel), F1xy, Immensity, Englezos, Marisa, R4v3n, Void, NotKernel, Smurf, Candy, Supermad, Antarctica, Evira

MY SUPPORT

I got help from multiple telegram guys for this.

Shoutout to @ishtiak02, @ComicoX, @logosA, Bruce Wayne, SSS, @Noobmaster69 @Lacentix @Raaj52 @nevoness @joshuah1971 and a lot of others teaching me about ROMs and answering my numerous questions.

I am using the Indian variant K20 pro (aka Raphaelin)

You can always ask in the Our Telegram Group, or me, or in the comments. (not allowed to link telegram group I think)

~FINISH

~Do Comment and Thank, it'll bump this guide to be noticed more, so others can find this guide and get help as well