According to the doctrine of the Catholic Church, the era of public revelation ended with the death of the last living Apostle.
A Marian apparition, if deemed genuine by Church authority, is treated as private revelation that may emphasize some facet of the received public revelation for a specific purpose,
but it can never add anything new to the deposit of faith.
The Church will confirm an apparition as worthy of belief, but belief is never required by divine faith.