Can dynamic QR codes be used offline?

No — a dynamic QR code needs an internet connection at scan time, because the phone must reach the redirect server to find out where the code currently points. No connection, no redirect, no destination.

Scanning itself works offline (the camera reads the pattern without any network), so the phone will decode the short URL — it just can't open it until it's online.

If your code must work with zero connectivity — WiFi login cards, contact cards at venues with poor signal, plain text instructions — use a static code with an offline payload: WiFi credentials, a vCard or raw text all live entirely inside the pattern and work with airplane mode on. That's a genuine advantage static codes keep over dynamic ones.