Historically, some very large Android OEMs based in China and selling in China also provided bootloader unlocking support in their devices including Xiaomi http

Historically, some very large Android OEMs based in China and selling in China also provided bootloader unlocking support in their devices including Xiaomi https://github.com/zenfyrdev/bootloader-unlock-wall-of-shame/blob/main/brands/xiaomi/README.md https://github.com/zenfyrdev/bootloader-unlock-wall-of-shame... and Oppo https://github.com/zenfyrdev/bootloader-unlock-wall-of-shame/blob/main/brands/oneplus/README.md https://github.com/zenfyrdev/bootloader-unlock-wall-of-shame... It doesn't have anything directly to do with GrapheneOS, and would have enabled custom OS support of any Android distribution.