Fr. Francisco de Vitoria explaining how Invincibly Ignorant people can be saved while Invincible Ignorance itself doesn’t save.

When we postulate invincible ignorance on the subject of baptism or of the Christian faith, it does not follow that a person can be saved without baptism or the Christian faith. For the aborigines to whom no preaching of the faith or Christian religion has come will be damned for mortal sins or for idolatry, but not for the sin of unbelief. As St. Thomas says, however, if they do what in them lies, accompanied by a good life according to the law of nature, it is consistent with God’s providence that he will illuminate them regarding the name of Christ.

Scott, James Brown; Vitoria, Francisco de (2000). The Spanish Origin of International Law: Francisco de Vitoria and His Law of Nations. The Lawbook Exchange, Ltd. ISBN 978–1–58477–110–4.