I didn't find a Windows machine, so tried to flash from Ubuntu.

I looked at flash-all.bat, and saw that basically all it does is:
fastboot -w update images.zip

So I unpacked 9.0.17-OnePlus6TOxygen_34_OTA_024_all_1909112343_d5b1905-FASTBOOT.zip on my Ubuntu machine and after booting the device into Fastboot mode, ran:

$ fastboot -w update images.zip 

Which seemed to be working, but then failed at:

...

Sending sparse 'vendor' 1/2 (785343 KB)            OKAY [ 32.142s]
Writing 'vendor'                                   OKAY [  0.001s]
Sending sparse 'vendor' 2/2 (31404 KB)             OKAY [  6.409s]
Writing 'vendor'                                   OKAY [  0.001s]
archive does not contain 'vendor_other.img'
Erasing 'userdata'                                 OKAY [  1.210s]

	F2FS-tools: mkfs.f2fs Ver: 1.14.0 (2020-08-24)

Info: Disable heap-based policy
Info: Debug level = 1
Info: Trim is disabled
Info: Set conf for android
	Error: Sparse mode is only supported for android
/usr/lib/android-sdk/platform-tools/make_f2fs failed with status 255
fastboot: error: Cannot generate image for userdata

I tried again, this time without -w:

$ fastboot update images.zip

This completed without error, however attempting to boot the device now gives me:

QUALCOMM CrashDump Mode
-----------------------

Attempted to kill init! exitcode=0x0000000b
                                           do_exit

Attempting to enter Recovery mode results in the same error, but I can still enter Fastboot mode, so the device is not bricked yet.

@MrT10001 said in OnePlus 6 android 11 OxygenOS11.1.2.2:

Thats for the OP6, not 6T. Slightly different ROM even though there is cross platform development.

Oh right, thanks.

@MrT10001 said in OnePlus 6 android 11 OxygenOS11.1.2.2:

@ginggs That rollback has worked for me (the OB25 rollback is for the OP6, not 6T).

Download the last Android 9 flashable zip from here.

On a Windows machine, open a terminal in the extracted folder and attach the device in fastboot mode. Then run the flash-all.bat file.

I will try when I get access to a Windows machine.
Thanks again!

@MrT10001 said in OnePlus 6 android 11 OxygenOS11.1.2.2:

@ginggs It should still work, however as we know, it also may not

On my Ubuntu Machine I have installed it using the snap store and the Edge version which is version 0.10.0. I use this version on my Windows machine as well.

Thanks! OK, I did:

$ snap refresh ubports-installer --edge
ubports-installer (edge) 0.10.0 from UBports refreshed

Unfortunately, the result was much the same.

The device rebooted to the Fastboot menu, and the Ubuntu Touch installer displayed "Cleaning up..." but nothing further happened.

I'm wondering whether I need to go back a step, and figure out why the Local Upgrade of OnePlus6Oxygen_22_OTA_054_all_1908302047_fulldowngrade_f019784c78234a67.zip does not work.

@MrT10001 said in OnePlus 6 android 11 OxygenOS11.1.2.2:

As you can see that is not displayed, so you must be using an older installer.

I have 0.9.7-beta from latest/stable channel installed. Which version should I be using?

@MrT10001 said in OnePlus 6 android 11 OxygenOS11.1.2.2:

Once your bootloader is unlocked you must reboot the device and set Android up again.

In Developer mode you must enable USB Debugging for the installer to see the device.

I had done that.

My first problem was that the "Allow USB debugging?" prompt was not appearing on the device after plugging it in. After several more attempts, it appeared and the Ubuntu Touch installer was able to recognize the device. (I think it may have been due to the device not having the correct date and time set, but am not sure).

After setting "Installation options":
Channel: 20.04/arm64/android9plus/stable
Wipe Userdata: Wipe personal data (required for new installs)
Bootstrap: Flash system partitions using fastboot

The device rebooted to the Fastboot menu, and the Ubuntu Touch installer displayed:

Cleaning up...
Formatting system partition

Nothing happened for about 20 minutes, until I gave up.

Hi, I recently acquired a OnePlus 6T with the intention of installing Ubuntu Touch. I used a BQ Aquaris E4.5 for a long time, but was in need of a hardware upgrade.

Thank you for your detailed instructions, but I've been unable to complete the installation, and still require some help.

@MrT10001 said in OnePlus 6 android 11 OxygenOS11.1.2.2:

Download the rollback build OB25 (OnePlus6Oxygen_22_OTA_054_all_1908302047_fulldowngrade_f019784c78234a67.zip) from the link here

My phone did not recognize this file or allow me to perform the Local Upgrade. I did verify the integrity of the downloaded .zip file.

I found this post, and was able to downgrade to Android 9, using the file Fulldowngrade_wipe_18801_181024_2027_user_MP2_release.zip recommended in this post:
https://forums.ubports.com/post/78512

Reboot to fastboot mode and Unlock the Bootloader - this involves having the ADB and Fastboot drivers installed on the PC and opening a terminal in the folder that contains them.

Run the command ./fastboot OEM unlock

I was able to perform the steps above, and the bootloader appears to be unlocked.

Start up the Ubuntu Touch installer and connect your device too it. Accept the dialogue box on the device for USB debugging. Follow the instructions on the installer.

The Ubuntu Touch installer no longer seems to be able to communicate with the phone. Developer Mode and OEM Unlocking are enabled, and I am able to transfer files. I tried transferring the file OnePlus6Oxygen_22_OTA_054_all_1908302047_fulldowngrade_f019784c78234a67.zip again, and can still not do a Local Upgrade.

Any suggestions for me please?