If you encourage using a wallet that supports OP_RETURN that might work. Most folks will probably be sending from an exchange though unless they have another hot wallet and most exchanges don't allow OP_RETURNs.
Your best bet is a LNURL-PAY QR code. It allows the sender to attach a message. Most lightning wallets and exchanges support it. Depending on the gift size, you'll want to provide an onchain address too.
OP_RETURNthat might work. Most folks will probably be sending from an exchange though unless they have another hot wallet and most exchanges don't allowOP_RETURNs.