Sorry, to break the suspense.
However, it seems the CPU is the SpacemiT Key Stone K1. Regarding their Git kernel repository, there is a milkv-jupiter.dts file in the arch/riscv/boot/dts/spacemit directory.
https://gitee.com/bianbu-linux/linux-6.1/tree/bl-v1.0.y/arch/riscv/boot/dts/spacemit