Sony used to be surprisingly good on this - but I'm uncertain what the current status actually is:

https://developer.sony.com/open-source/aosp-on-xperia-open-d...

> Note: New devices XQ-CT62 (1Ⅳ US variant) and XQ-CQ62 (5Ⅳ US variant) do not support bootloader unlock.

https://xdaforums.com/t/unlock-bootloader-and-root-guide-xpe...