[Google Pixel 3a XL Guides, News, & Discussion] KJ7LNW:
I've been trying to find a good phone for my wife that is officially supported by LineageOS and settled on the Pixel 3a. If you're thinking of purchasing this device, make sure the listing says that it has an UNLOCKED BOOTLOADER. Just "unlocked" doesn't cut it, you'll probably get a phone that works on any carrier but won't allow an OEM unlock. Third time is the charm, we finally ordered from eBay; the listing said unlocked bootloader, and it was.

I had some trouble getting started so hopefully this will help others. This guide will probably work on the Google Pixel 3a (sargo, not XL), and possibly other Pixel devices as well assuming you adjust your release version appropriate to your model.

Note that TWRP doesn't work well (or at all), and don't even try because the Pixel 3 and newer are slot A/B devices so LineageOS uses their own recovery to manage switching between boot slot A/B during update. (Of course, if you do get TWRP working, then I do prefer it so let me know how!)

Enable developer mode

OEM Unlock: method 1, method 2

Unlock the bootloader:

adb reboot bootloader

fastboot flashing unlock

Install the latest android platform tools for fastboot and adb:

https://developer.android.com/studio/releases/platform-tools

Install the official Android 11:

https://developers.google.com/android/images?authuser=3#bonito

Agree to terms and conditions

Download the latest v11 zip (RQ3A.211001.001, Oct 2021)

Unzip and run:

Windows: flash-all.bat

Linux: ./flash-all.sh

Repeat #3 above if necessary

Download and transfer LineageOS 18.1:

https://download.lineageos.org/bonito

Download the latest recovery .img to your desk

Download the latest .zip to your desk

Install the recovery image:

fastboot flash boot_a lineage-18.1-20211023-recovery-bonito.img

fastboot flash boot_b lineage-18.1-20211023-recovery-bonito.img # (might not need this one)

Reboot to recovery (may need to power off first)

From the Phone: In recovery it should show the LineageOS icon:

Advanced->Enable ADB (may not be necessary)

Apply Update

Apply from ADB

From your desk:

adb sideload lineage-18.1-20211023-nightly-bonito-signed.zip

If you get errors like error: protocol fault (no status) then your version of adb is too old.

It should say Total xfer: 1.00x but the official LineageOS installation docs say that it might hang at 47% and that is ok because it is done transferring to the phone at that point.

From your phone:

If you want the Google Apps add-on on your device, you must follow this step before booting into LineageOS for the first time!

If so, then tap Apply Update->Apply from ADB and follow Google Apps .zip install notes below in #7.3

If not, then tap the left return arrow and then tap "reboot now"

Optional ZIPs:

If you are already in recovery, go to step #7.2. Otherwise, get into recovery. If you already booted into LineageOS, then I find it easiest to reboot into recovery by enabling "Advanced Restart" :

Systems->Advanced->Gestures->Power->Advanced restart

Then hold down the power button and select Power->Reboot->Recovery

To install zips:

First mount /mnt/system: Adbanced->Mount/Unmount System

This is necessary because the Pixel is a A/B boot slot device and not all .zip's will know how to mount.

Use adb sideload <filename.zip> as in #6.4 above (but with the .zip you want!)

You may be prompted on your phone to install even though the signature is untrusted.

Download the latest Google Apps for arm64. (Do this before booting LineageOS for the first time!)

Most people recommend MindTheGapps,however:

Because the Pixel is a A/B boot slot device, MindTheGapps doesn't know how to mount /mnt/system so it fails.

This is probably a bug in MindTheGapps, if you find a way to fix it let me know.

Others like OpenGApps.

I installed this one, but for some reason it didn't work the first time. It did the second! Maybe I missed something.

Well Play Store is hanging, so trying MindThe Gapps

Root your device with Magisk:

Download the latest Magisk APK:

Note that the .apk is also a .zip, so rename it if you must (but I didn't need to).

Enable adb

Install the apk:

adb install Magisk-v23.0.apk

Troubleshooting:

LineageOS recovery doesn't like to install multiple zips at once. If you get the error adb: sideload connection failed: closed then click the left back arrow, then again folow steps from 6.4

Try factory reset if you have boot issues the first time