@ezst036 Wow, I found the OP6T one of the easiest phones to install! I'll put the next bit in bold to help others:
If the device is at the bootloader (fastboot mode) and connected and you start the installer, the installer will pick it up as example "sdm845". If you know which device you have manually select it from the drop down list in the installer and follow the on screen instructions.
The bootloader must be unlocked to install Ubuntu Touch and if the instructions indicate a specific version of Android must installed before, install that version, boot into it and set it up, enable developer mode and ADB/USB debugging before starting the installer. The reasons for the specific version of Android has to be installed is for things like Vendor BLOBS, specific bootloader, specific kernel.
To install UT on the OP6T I have always had to downgrade the Android version to Android 9 using this file
Fulldowngrade_wipe_18801_181024_2027_user_MP2_release.zip
This can be obtained from here. The link is still active at this date (11th February 2024).
Download it to the root of the device i.e. connect the device to the PC and set the USB connection to file transfer and copy the zip (STILL zipped) file to the device - NOT in a folder (i.e. the root of the device). Once done then go to Settings, System, System updates and with the cog symbol on the top right, choose Local Install and let it do it's thing. It will take about 15 minutes, reboot and leave you at the Android set up screen.
Set up Android again, and enable Developer options and ADB?USB debugging. Reboot to the bootloader.
Unlock the bootloader using fastboot oem unlock.
Reboot the device and set Android up again, enabling ADB/USB debugging.
Connect it to the PC and run the Installer.
The installer will then reboot the device and do most of the work for you. You will at one stage have to boot into recovery, the installer will do the rest.
@ezst036 You may have had issues due to the device being T-Mobile, but I have had many locked devices that I have installed UT to and it was only SIM locked, the UT install always went through.
If the device reboots and you get a message saying "Qualcomm Crash Dump", power off the device, charge the battery for a bit and boot it up again.
The stability of the device is not quite there yet, mainly due to the issue across devices with UT draining the battery. There is an app called BatterySaver for 20.04 by Lionel Duboeuf that will help.
I have no bricked devices due to installing UT (yet)!