[Huawei P20 Pro Guides, News, & Discussion] asozio:
I unlocked my P20 Pro using a hardware testpoint, the HCU software, and a lot of time. I would suggest reading the information below, gathering all the tools/software/ROMS/IMGS you need and asking any questions before you purchase a licence or attempt this process.

WARNING!!!! THIS WILL ERASE YOUR PHONE COMPLETELY!!!

I would suggest making sure if you are going to purchase the 3 day license (this is what I did) that you are available to work on the phone for a couple of days (maybe buy it just before the weekend?) as if you run into any issues you won't have much time to fix them.

WARNING!!!! THIS WILL ERASE YOUR PHONE COMPLETELY!!!

BE CAREFUL TO PURCHASE THE THREE DAY LICENSE AT THE CHECKOUT NOT THE CREDITS (I MADE THIS MISTAKE AS YOU CAN PROBABLY TELL FROM THIS THRED)

Otherwise, the steps I went through are below, as well as some of the links to things I found helpful during the process:

1. SOFTWARE VERSION - It was not possible to unlock the bootloader on version 10 of the OS, so you will require HiSuite (https://consumer.huawei.com/au/support/hisuite/) to downgrade or dc-phoenix to flash an earlier version. I used 9.0.0.168 for my phone (Model: CLT-L29) so will reference that in all the steps below, but use the corresponding version for your phone (whichever you downgrade to from HiSuite should be fine?)

2. TESTPOINT - I used the hardware test point (next to the camera once the back cover is removed) but apparently this is possible using the software test point process (I am uncertain of the exact process for this, but there is a guide on the dc-unlocker site somewhere)

3. ADP/FASTBOOT RECOVERY UNLOCKING - Once the HCU software has provided a new code (or if you already have one) you can use fastboot oem unlock <code> where the <code> is the bootloader unlock code to unlock.

WARNING!!!! THIS WILL ERASE YOUR PHONE COMPLETELY!!!

4. ALTERNATIVE OS INSTALLATION - In my case I installed LineageOS 16 using an old guide (https://web.archive.org/web/20210726230701/https://depl0y.com/posts/P20-Pro-LineageOS-Guide/) which will only work (even the official version) if you patch the Lineage installation (update-script requires editing or replacement)

Install TWRP

Enable USB debugging

adb reboot bootloader

fastboot flash recovery_ramdisk twrp-3.7.0_9-0-charlotte.img

Hold VOL-UP & VOL-DOWN

fastboot reboot

You should now be in TWRP.

Flash LineageOS (and gapps)

In TWRP go to Advanced > ADB Sideload

adb sideload adb sideload lineage-16.0-20210211-nightly-charlotte-signed-modified.zip

adb sideload open_gapps-arm64-9.0-nano-20220215.zip

In TWRP go to Reboot > Bootloader

fastboot flash recovery_ramdisk RECOVERY_RAMDISK_9.0.0.168.img

fastboot reboot recovery

You should now be in the stock recovery. If not, boot into stock recovery

Select Wipe data / factory reset

Reboot system now

THE P20 WILL ONLY BOOT WITH THE STOCK RECOVERY, SO REPLACE IT AFTER USING TWRP

5. WEBVIEW FIX FOR GOOGLE APPS - DO NOT SET UP WIFI DURING INSTALL!

Download com.google.android.webview.apk from apkmirror and copy to the device. Install using the default file manager and reboot the phone. Sign in to Google and update webview, google apps, etc

6. ROOT ACCESS - MAGISK

Install apk (copy to storage and run from files) for Magisk and patch RECOVERY_RAMDISK_9.0.0.168.img.

Reboot into bootloader and flash to recovery: fastboot flash recovery_ramdisk RECOVERY_RAMDISK_9.0.0.168_magisk_patched-25200_8akQl.img

TO BOOT PHONE WITH ROOT BOTH VOLUME UP AND POWER BUTTONS NEED TO BE HELD AT STARTUP!