There’s definitely a larger shipment going to the stores, since they’re showing pickup availability on the 19th, while online orders are showing shipment dates around the 25th. For example, I placed my order right at launch—I got the confirmation email from Apple at 5:01 AM—and still ended up with a delivery date of the 25th.
It seems pretty clear that Apple anticipated limited stock on the iPhone Pro Max, especially in Orange, and reserved more units for in-store pickup. My guess is they’re doing this to drive people into the stores, since once you’re there, you’re more likely to buy accessories like cases, chargers, or AppleCare.
What doesn’t make sense is why they wouldn’t fulfill online launch-day deliveries on the 19th. Apple has updated shipping windows in the past after adjusting inventory, so I’m hoping they’ll do the same here.