[OnePlus 6T  Questions & Answers] QUDDY:
I've been following this guide with the aim of installing lineageos on a 6T I just bought: https://lineageosroms.com/fajita/#installation.

I downloaded the following files in advance:

copy-partitions-20200903_1329.zip

lineage-18.1-20211230-nightly-fajita-signed.zip

lineage-18.1-20211230-recovery-fajita.img

I have followed all the steps up to and including steps 6 of part 'Temporarily booting a custom recovery using fastboot'. The last part that appeared to run successfully was step 5 e.g.: fastboot flash boot lineage-18.1-20211230-recovery-fajita.img

Here is the output of the commands run on the host (serial number redacted):

adb reboot bootloader

➜ fastboot devices

******* fastboot

➜ fastboot oem unlock

OKAY [ 0.036s]

Finished. Total time: 0.036s

➜ adb reboot bootloader

➜ fastboot devices

******** fastboot

➜ fastboot flash lineage-18.1-20211230-recovery-fajita.img

unknown partition 'lineage-18.1-20211230-recovery-fajita.img'

fastboot: error: cannot determine image filename for 'lineage-18.1-20211230-recovery-fajita.img'

➜ fastboot flash boot lineage-18.1-20211230-recovery-fajita.img

Sending 'boot_a' (65536 KB) OKAY [ 1.543s]

Writing 'boot_a' OKAY [ 0.332s]

Finished. Total time: 1.973s

➜ fastboot devices

******** fastboot. ### This is where I just see the message about the OEM being unlocked and integrity.

➜ adb sideload copy-partitions-20200903_1329.zip ## I ran this even though I just saw the integrity message in the hope it would then enable me to select 'Apply Update'.

adb: sideload connection failed: no devices/emulators found

adb: trying pre-KitKat sideload method...

adb: pre-KitKat sideload connection failed: no devices/emulators found

➜ fastboot devices

******** fastboot

NB I once accidentally wrote fastboot flash lineage-18.1-20211230-recovery-fajita.img instead of fastboot flash boot lineage-18.1-20211230-recovery-fajita.img (i.e. I missed off the 'boot'). However, as I got the immediate error "fastboot: error: cannot determine image filename for 'lineage-18.1-20211230-recovery-fajita.img'" I suppose it was a no-op and hopefully didn't do any harm.

The problem is that when I then booted into the phone with volume down and power (step 6) I just got a screen with a message about the OEM being unlocked and phone integrity.

I powered the phone off after waiting a while with volume up and power. Then powered on. Same message. Since then I've tried powering off and on with both volume up and volume down and power. I get into a mode where I can select start, restart boot loader, recovery mode and power off.

View attachment 5498107

As I understood I'm trying to get into 'recovery mode' I selected that, but that just restarts the phone. I think that just took me back to the integrity message and at that point I ran the command adb sideload copy-partitions-20200903_1329.zip in the hope it would bring up the option to apply the update. However, now whenever I restart the phone I don't see the integrity message, just the 'options' menu (please see 'start' option above). I don't see the OEM unlocked/integrity message any more regardless of how I start the phone.

I have now tried basically all the options including restart the bootloader. All lead back to the same screen. When I have the phone connected to my mac via usb, I can still at least see it with fastboot devices:

fastboot devices

******** fastboot

As the guide I'm following doesn't show what you ought to see at each step I'm not sure what should have happened on step 6 when booting into recovery mode (this is my first flash) but as the guide says

'On the device, select “Apply Update”, then “Apply from ADB” to begin sideload.' I'm guessing it should at least have booted into a UI different to the one I'm seeing.

Is there anything I can do now? Should I try flashing another recovery image? Re running anything? Is it 'bricked'?

Really appreciate any guidance.