I think they're pretty open? Atleast I've seen a few good custom roms for Sony Phones, like DivestOS (before it died). I don't know if they stopped doing that recently.
I think Sony Xperia phones.
https://m.gsmarena.com/sony_xperia_1_vii_5g-13843.php
Snapdragon 8 Elite. Release May 13, 2025.
I think they're pretty open? Atleast I've seen a few good custom roms for Sony Phones, like DivestOS (before it died). I don't know if they stopped doing that recently.