What I mean by objective duties is that there are moral rules that could not be reasonably rejected and would therefore be a part of the social contract (restrictions on murder, slavery, discrimination etc.). This is in some sense metaphysical and some sense dependent on human nature.

The is-ought problem can't be bridged, however the mere pursuit of normativity is enough for reason to bind an agent's freedom and place them under the moral law. And this moral law is objective. Yet this is the whole mission of my substack, so I'll have much more to say about this.