In-store iPhone trade-in after online pre-order pickup

Yes, you can generally bring your old iPhone directly to an Apple Store for an in-store trade-in when picking up an online pre-order, even if you selected the mail-in option at checkout. However, experiences can sometimes vary by location or specific store policy during busy launch periods. 

For me when I traded in my 15 pro last year, I needed to return a week later to complete the trade in process

4Wolfie wrote:

Can I bring my old iphone for trade in directly to apple store, after pre-order online new iPhone to (pickup in store) instead sending old by mail ?

In my experience, yes. Assuming the store isn’t overrun. Keep your receipts.