What is the voltage of an electrochemical cell at equilibrium?
There is a cell equilibrium and 2 independent half-cell equilibrii.
There are 2 half-cell equilibrium potentials and a cell open voltage as EMF as the difference of 2 half-cell equilibrium potentials, because the cell in the whole is not in equlibrium.
When a cell gets into equlibrium as the whole system, the cell voltage is zero.