I shouldn't be surprised that they have some documentation on this particular topic:

https://docs.flipper.net/one/cpu-software/rk3576-mainlining

But I'm guessing it's part Rockchip being more Linux-friendly than Broadcom and a group with a specific goal of a more open boot process. Or more simply, just different objectives or priorities than others in the space. And just to be clear, it's not as if they have everything working completely in vanilla Linux, they list peripherals or functions that aren't supported (NPU, video encoder, CSI).