Is it permissible or forbidden to legalize or officially certify contracts for the sale of real estate and equipment acquired through interest-based loans, and to legalize the mortgage of the same real estate or equipment in favor of the interest-based lending bank?

If the intent of the question is to notarize usurious contracts or to notarize a mortgage for a bank in a usurious loan, then that is Islamically prohibited, because it constitutes an affirmation of evil and assistance in it. However, if a person took a usurious loan and purchased a property, and then wished to sell it and notarize this sale, there is no harm upon the one who performs the notarization; because the borrower who engaged in usury is considered the legal owner of the property, despite the sin of usury.