Rockchip devices have stellar mainline (that chip rk3588 doesn't have it yet), for business reasons (radxa relies on it for industrial support, Chromebooks push mainline very heavily). I can't speak for this new one, but previous rockchip flagship (rk3399) have exactly one binary blob, which is used for display port over usb-c. Everything else is supported as open source, and mostly supported mainline (Linux and uboot and atf)