set_to_none=True and accumulate_grad_batches
Is it possible to use automatic optimization with accumulate_grad_batches and performance trick zero_grad(set_to_none=True)?
Yes, you can override the zero_grad hook in LightningModule
    def optimizer_zero_grad(self, epoch: int, batch_idx: int, optimizer: Optimizer, optimizer_idx: int):
        optimizer.zero_grad(set_to_None=True)