Is it necessary to use a WordPress nonce when allowing users to download public data?

Nonces are used to verify that a request is allowed from the sender. For public data, all GET requests are allowed, if they match existing public content.

So no, do not use a nonce for that. You have nothing to do if the nonce validation fails. That’s always a good indicator for unnecessary information.

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)