Update LineageOS from 16.0 to 17.1 on the OnePlus 6T (fajita)

Updating from 16.0 to 17.1 on A/B devices without data loss can be tricky, especially with the OnePlus 6T…

Here are my upgrade notes.

First, ADB and fastboot should be functional android-tools)

An up-to-date Oxygen OS has to be sideloaded on both slots (a/b), this will bring updated firmwares and also, the compatibility with LineageOS 17.1. The easiest solution is to sideload the Oxygen OS zip on one slot, and then sideload copy-partitions.zip in order to copy Oxygen OS to the other slot.

Then, we can sideload LineageOS 17.1 and Open Gapps (arm64), you can download the arm64 / nano package on opengapps.org

You will need:

• an up-to-date Oxygen OS build
• an up-to-date LineageOS build
• the file copy-partitions.zip

Because of compatibility issues, we need to use unofficial recovery builds of twrp:

• TWRP 3.3.1-32 Pie Unofficial by mauronofrio
• TWRP 3.3.1-32 Q Unofficial by mauronofrio

Downloads all these files, and start this procedure:

adb reboot bootloader
fastboot boot twrp-3.3.1-32-fajita-Pie-mauronofrio.img
adb shell twrp sideload
adb sideload OnePlus6TOxygen_34_OTA_044_all_2002220041_110bb9052a994b6f.zip
adb reboot bootloader
fastboot boot twrp-3.3.1-32-fajita-Q-mauronofrio.img
adb shell twrp sideload
adb sideload copy-partitions.zip
adb shell twrp sideload
adb sideload lineage-17.1-20200412-nightly-fajita-signed.zip
adb reboot bootloader
fastboot boot twrp-3.3.1-32-fajita-Q-mauronofrio.img
adb shell twrp sideload
adb sideload open_gapps-arm64-10.0-nano-20200412.zip
adb reboot