What is the ruling on not fulfilling a covenant made with Allah not to look at a specific thing, knowing that this looking was a means of protecting oneself from fornication?

As long as you are unsure whether you uttered an oath of divorce or an oath by Allah, divorce does not occur, because divorce is not established with doubt, and the default is the exoneration of responsibility. As for making a covenant with Allah not to look at a specific thing and then falling into it, it is more cautious to offer expiation for breaking an oath (kaffarat yamin (definition)). You must also repent from looking at what is forbidden, and know that the argument that forbidden glances protect you from zina (unlawful sexual intercourse) is false; rather, it is a cause for falling into it. Indeed, a person guards against zina through marriage or through fasting, while safeguarding their hearing and sight.