The physical box with the key ships at release. You usually won’t have it the second the game goes live.
Some people are ok with that. Others want the physical goodies but also to play right away. Those folks usually purchase a digital version too.
Blizzard understands that is not ideal and does have some means of providing funds back to people. You can get the digital version back as Bnet balance you can spend on game time or something else.
If you buy Dragonflight (Base, Heroic, or Epic) on the Battle.net Shop and then redeem a Collector’s Edition code, we will automatically refund you the cost of your digital purchase in Battle.net Balance, as long as you redeem the Collector’s Edition code before December 31, 2023.
There was a pinned thread about it too but that seems to be unpinned.