[Huawei Mediapad M3 ROMs, Kernels, Recoveries, & Ot] diztorded:
Wow... What a journey!! Between partial directions and soft-bricking, I never thought I would get it running. Since I went through all the pain, I thought I would post my steps.

These steps require a Windows PC!!

Also, I do not take credit for any of the hard work that all the amazing people did on this. I am just listing out my steps. Please take the time to drop a kudos to the authors of the links I am sharing.

This was my starting point for reference: Lineageos 17.1 for Huawei Mediapad M3.8.4

Getting things ready:

Get a SD card for your Mediapad

Download the following onto your computer

TWRP 3.3.1-1

Huawei MediaPad M3 BTV-W09C100B308CUSTC100D001 Firmware 7.0.0 r1 EMUI5.0 05013XKP.zip(Stock firmware just in case you need it)

Unzip this into a folder (ie /temp)

Go into /temp/Software

Extract SDupdate_Package.tar.gz

Copy the entire dload folder onto the Mediapad SD card

Download DC Unlocker and extract it onto your computer

Install the USB drivers for Windows/Mac: Huawei HiSuite (I used version 9.0.3.300)

Install ADB and Fastboot in your computer using these instructions: ADB/Fastboot Instructions

Copy TWRP to the ADB folder

Download the following onto your Mediapad SD card

LineageOS-17.1-BTV_2021-03-19.zip

boot_w09_ten_20210313.img

GApps - ARM64, 10.0, nano

It's show time:

On the Mediapad, enable Developer Options

Go into Settings

Goto About device

Tap Build Number 7 times

Back out one level and select Developer Options

Enable OEM Unlock

Enable USB Debugging

Plug your USB cable into your computer and Mediapad

You should get a popup about trusted connections, if you do not, verify step 2.2 is done

Select to always trust the connection

Launch a Command Prompt and navigate to the ADB folder

Enter the following command to see if the tablet is configured properly: adb devices

If this fails, verify drivers, USB cable is capable to do data connections, and the tablet is configured

Follow the instructions here for Unlocking the Bootloader and Flash Greatslon TWRP: TWRP Instructions

Only use the files I linked above

You do not need to install Magisk

Disconnect the USB cable

Boot into TWRP

Select Wipe then select Format Data

This will format the table and remove the encryption (VERY important step)

Once finished, back up to the main screen and select Install

Click Select Storage and select Micro SD card

Also verify there is a size other than zero next to Internal storage

If it is zero, then redo step 7

Select the LineageOS zip file

If you want to add some of the Google apps, then select Add more Zips

Select the open_gapps zip

Swipe to flash

There will be an error about 3rdModem. This can be ignored

Back out and select Install Image

Select the boot_w09_ten image

Select Reboot

You are now finished! Congratulations. I have included some extra steps below to help out with two issues I ran into. They do not need to be followed unless you want to.

Restore Stock Image:

Turn off the tablet

Hold down the up and down volume buttons and turn the tablet back on

This will reload the image located in the dload folder on the SD card.

Once in LineageOS, Google will complain about not trusting the tablet. This is fixed by

Enable USB debugging on the tablet

Enable Rooted Debugging on the tablet

Connecting the USB cable to the tablet and computer

Trust the connection on the tablet

Open a command prompt on the computer

Navigate to the ADB folder

Do a "adb devices" to verify the tablet is connected

Use the following commands

adb root

adb shell

sqlite3 /data/data/com.google.android.gsf/databases/gservices.db "select * from main where name =\"android_id\";"

This will give you a long code, use it here to register your device:

https://www.google.com/android/uncertified/

This will take about 30 minutes or so...