What is the difference between full duplex and dual simplex?
Dual Simplex means the 2 lanes are simultaneous unidirectional, but hardware may be selected in either direction.

Full Duplex is also simultaneous unidirectional but by hardware design limited to opposing directions such as RS-232, USB 2

So Dual Simplex could be dual lanes for same direction for bandwidth doubling doubling such as USB 3 or configured as Dual Simplex in opposite directions.