Does a QR code need Wi-Fi to work?

No — reading a QR code needs no Wi-Fi or mobile data at all: the camera decodes the pattern optically, entirely on the phone. What happens next decides whether a connection is needed.

Codes that work with zero internet: Wi-Fi codes (they hand over network credentials), contact cards (vCard), plain text and phone/SMS codes — their entire payload lives inside the pattern.

Codes that need a connection after scanning: anything opening a web page, including all dynamic codes (the phone must reach the redirect server to resolve the destination). So a menu code needs signal to load the menu; a Wi-Fi code is the neat exception that provides the connection. Planning for a low-signal venue? Prefer offline payload types, or make sure the venue Wi-Fi code is the first thing guests scan.