Without a lens (therefore no serial number), there is no cashback.

It could still be that your order is cancelled by Digitec for whatever reason. In such a case (which I admit is unlikely), why should you be able to claim a cashback without having received the goods?

If the cashback is very important to you, e.g. for price reasons, I would simply cancel the lens at Digitec shortly before 31.7. if the delivery date is still very uncertain. The next cashback campaign from Sony will not be far away.

Then you are out of luck. You even have to send a photo with the lens in your hand. But I wouldn't recommend this lens anyway. Honestly.