When I got my iPhone 14 I remember some people coming without ordering first. Most of them didn’t get an iPhone but the lucky ones that dad didn’t have much of a choice when it comes to color or storage size.
Your best chance, as other threads have already covered, is to check stock at 5-6am on launch day for the store you want to pick up at. Order from the app to be picked up in store. There's a chance that they're all going to go that way and nothing for walk-ups on a launch day. At least for the Pro Max.
If you were getting a 15 or a 15 Plus, I am pretty sure you could be accomidated. If you want the pro or pro max, better be the first in line and happy with any color or storage option.