Cannot install UT on OP6T

[ubuntoutou]

I can't install Ubuntu Touch on my OP6T. The installer is stuck at

"Waiting for device... Fastboot is scanning for devices".

This happened after the phone became bricked as it booted and still boots with the following message:

QUALCOM CrashDump Mode
Attempted to kill init! exitcode=0x0000000b
complete_and_exit

I bricked the device after running into difficulty trying to install TWRP first:

fastboot flash recovery twrp.img
Writing 'recovery' FAILED (remote: '(recovery_b) No such partition')

Then I read https://android.stackexchange.com/questions/209673/why-cant-i-write-to-recovery-using-fastboot-on-a-b-device which advised to run instead

fastboot boot twrp.img

That is when the phone became bricked...