The way to get it working with a normal map passed in is to change the “Blend Mode” to “Additive” (make sure you’re clearing the render target to 0,0,0,1) - this seems to fill the alpha channel correctly.
Normal Maps are stored as values between -1.0 and 1.0 - so to get that information out from an “unlit” material - you need to multiple the normal value by 0.5, then add 0.5 to make it range between 0.0 and 1.0:
