The Oriental Orthodox say Jesus has One Nature, but what they mean by it amounts to what all Chalcedonian Christians believe.
There have been numerous Christological declarations between Rome, the Eastern Orthodox, and the various Oriental Orthodox jurisdictions to that effect.
Some more militant OOs accuse Chalcedonians of being “Nestorians”, though.
It is my understanding that they believe the humanity and divinity of Jesus are perfectly joined in one nature, The Logos or Incarnate Word. Not that they reject either His humanity or His Divinity.