The Catechism discusses “invincible ignorance” here:
IV. ERRONEOUS JUDGMENT
1790 A human being must always obey the certain judgment of his conscience. If he were deliberately to act against it, he would condemn himself. Yet it can happen that moral conscience remains in ignorance and makes erroneous judgments about acts to be performed or already committed.
1791 This ignorance can often be imputed to personal responsibility. This is the case when a man "takes little trouble to find out what is true and good, or when conscience is by degrees almost blinded through the habit of committing sin."59 In such cases, the person is culpable for the evil he commits.
1792 Ignorance of Christ and his Gospel, bad example given by others, enslavement to one’s passions, assertion of a mistaken notion of autonomy of conscience, rejection of the Church’s authority and her teaching, lack of conversion and of charity: these can be at the source of errors of judgment in moral conduct.
1793 If - on the contrary - the ignorance is invincible, or the moral subject is not responsible for his erroneous judgment, the evil committed by the person cannot be imputed to him. It remains no less an evil, a privation, a disorder. One must therefore work to correct the errors of moral conscience.
https://www.vatican.va/archive/ccc_css/archive/catechism/p3s1c1a6.htm
Jimmy Akin also discusses “vincible” and “invincible” ignorance here:
When a person commits a sin through invincible ignorance it is called a “material” sin (as opposed to a “formal” sin which occurs when a person freely chooses to sin knowing in their conscience that the act is sinful). However, as Pope St John Paul II notes (in Veritatis Splendour at 51) even when a person commits a material sin through invincible ignorance, it still damages the “communion of persons” (so every person should do their best to form their conscience properly):
“When [people] disregard the law, or even are merely ignorant of it, whether culpably or not, our acts damage the communion of persons, to the detriment of each.”
http://www.vatican.va/content/john-...hf_jp-ii_enc_06081993_veritatis-splendor.html