Can I recover my phone? / How I most likely bricked my F5122. - Sony Xperia X Questions & Answers

Hi all,
it seem that I bricked my Sony Xperia X F5122.
I'll try to explain all the steps I took as detailed as possible hoping that I can recover my phone with your help somehow.
Steps:
- unlocked bootloaded following official Sony documentation (1)
- extracted TA partition
- installed Sailfish X according to official documentation (jolla.com/sailfishx-linux-instructions/)
- successfully ran Sailfish X for 1,5 years with all things functioning
- decided to reflash stock android to give phone to my daugther
- connected phone to Win10 PC in flashmode (Volume down while connecting to PC)
- started EMMA tools from Sony
- it detected the phone and presented several flashable images
- started flashing of latest image which finished successfully
- after flashing the phone boot-up failed with a message that the image is broken
- restarted phone and tried to get into flashmode again
- flashmode failed with LED blinking in a strange colors code (2)
- booted into fastboot mode (volume up while connecting to PC)
- booted TWRP (3) successfully
- flashed TA partition back to phone using abd mode available thanks to TWRP as I thought that it will enable the flashmode again
Current state:
- can set phone into fastboot mode
- all actions initiated with fastboot command are answered with "remote: Command not allowed" (4)
- tried to flash OEM using all available AOSP images from Sony (5)
- tried to unlock phone again (6)
- tried to boot TWRP image again (7) results in error "Your device has failed verification and will not work properly."
- cannot set phone into flashmode with LED blinking described above
- when booting phone the following error message is shown: "Your device has failed verification and will not work properly."
- when connecting to PC without any keys pressed, the same LED blinking is happening (2)
I assume that the commands are rejected due to enabled bootloader lock because of flashing the TA partition.
As no image I tried to run boots up due to verification error I cannot unlock the bootloader via developer settings thus not clear the TA partition again.
I also assume that I could flash the stock Xperia X image when I could enter the flashmode.
1) Does anyone of you know a way to unlock the bootloader via USB port?
2) Does anyone maybe know a boot image which succeeds verification and I could boot using fastboot mode?
(1) developer.sony.com/develop/open-devices/get-started/unlock-bootloader/how-to-unlock-bootloader/#tutorial-step-1
(2) dark red (~1 second), light red (~1 second), green (~3 seconds), yellow (< 1 second), restart with dark red
(3) twrp.me/sony/sonyxperiax.html
(4) several command outputs:
Code:
$ fastboot flash oem SW_binaries_for_Xperia_AOSP_N_MR1_3.10_v13_loire.img
target reported max download size of 536870912 bytes
sending 'oem' (164639 KB)...
OKAY [ 5.194s]
writing 'oem'...
FAILED (remote: Command not allowed)
finished. total time: 5.198s
(5) developer.sony.com/develop/open-devices/downloads/software-binaries
(6) unlock command:
Code:
fastboot oem unlock 0x<valid-unlock-code>
...
FAILED (remote: Command not allowed)
finished. total time: 0.004s
(7) boot TWRP
Code:
fastboot boot /home/aa_ulm/Downloads/twrp-3.3.1-0-suzu.img
downloading 'boot.img'...
OKAY [ 0.704s]
booting...
FAILED (status read failed (No such device))
finished. total time: 12.245s