https://wiki.postmarketos.org/wiki/Sony_Xperia_T3_(sony-seagull)

Hardware
Chipset Qualcomm MSM8928 Snapdragon 400
CPU Quad-core 1.4 GHz
GPU Adreno 305
Display 720x1280 TFT
Storage 8 GB + SD card
Memory 1 GB

https://developer.sony.com/develop/open-devices/get-started/unlock-bootloader/

Please note! It will only be possible to unlock the boot loader for certain releases. You can check if it is possible to unlock the boot loader of your device in the service menu by following the steps below:

    In your device, open the dialer and enter ##7378423## to access the service menu.
    Tap Service info > Configuration > Rooting Status. If Bootloader unlock allowed says Yes, then you can continue with the next step. If it says No, or if the status is missing, your device cannot be unlocked.

*#*#7378423#*#*

upstream source for android? https://github.com/Sony-Yukon

https://elinux.org/Sony_Debug_Assist_board