Is it obligatory to seek forgiveness for someone who wrote a paper that did not conform to the subject matter they intended to study at another university as a visiting student, and then graduated based on it?

If the second university accepts the course and approves its study, and the student is examined in it and passes, then there is no objection to that from the perspective of graduation, even if the approval was obtained through mediation. The decisive factor is the student's success in the courses assigned to him without cheating or forgery. If the approval process involved undue mediation or bribery, then one must seek forgiveness and not repeat such an act.