Gibbs energy and chemical equilibrium : false proof of spontaneous generation, but why?
Within the context of the equation in question, $\Delta G$ refers to the change in free energy between two specific thermodynamic equilibrium states:

State 1:  Stoichiometric quantities of pure reactants in separate containers at temperature T and individual specified pressures

State 2:  Corresponding stoichiometric quantities of pure products in separate containers at temperature T and individual specified pressures

In the case of $\Delta G^0$, the specified pressures are all 1 atmosphere.  This means that Q = 1, and $\Delta G =\Delta G^0$.

If the specified pressures in states 1 and 2 happen to correspond to the partial pressures of an equilibrium mixture of reactants and products, $\Delta G$ will be equal to zero.  In this case, if one had an equilibrium mixture of the reactants and products, the partial pressures in the equilibrium  mixture could also be held in equilibrium through individual semipermeable membranes with the gases in the separate containers of reactants and products (with no tendency for the reactants or products to enter or leave the reaction mixture through the semipermeable membranes).