Clearly, it's manual...but how? Just push it back and forth or does it lock, etc? Any pictures of that yet? Honestly, the warranty is so awesome from Rivian, I'm not too worried about the power cover...
Much like the explore package or the mac pack, the manual cover effectively doesn't exist yet. I don't think they've built a single truck without the powered tonneau.
But it's pretty clearly described as several pieces, you just have to click Learn More in the configurator: