Yeah so uh, Sony is super weird. There is the production side of Sony, and the developer side of Sony. They barely coexist, they are two completely different minds. Think I'm exaggerating? They have two bootloaders, one for developers, one for production. (The led changes color). Once you have unlocked your bootloader, you have to download and use a different flash tool to flash Sony's ROM. They are not available on the same page. That being said: - the "production" side is a meh OEM. Usually only one major upgrade, annoying lock-ins - the developer side is amazing. They make contribution to mainline Linux, they provide AOSP build trees, they upgrade major Linux kernel versions, their AOSP build tree is much more open source than Google's, they provide very clean fixes for stupid Qualcomm issues that is not fixed even on Pixels, they provide more android major upgrades

So yeah, weird. I believe their AOSP side is funded by some governments who want the most maintainable and auditable Android on their devices