code: def _step_envs(self, action):
      
      self._frame_counter += 1
      real_env_step_tuple = self.real_env.step(action)
      sim_env_step_tuple = self.sim_env.step(action)
      self.sim_env.add_to_initial_stack(real_env_step_tuple[0])
      return self._pack_step_tuples(real_env_step_tuple, sim_env_step_tuple)
docs: Perform step(action) on environments and update initial_frame_stack.