Is the loan taken from SAB Bank as part of the "SAB Amanah" program considered usury, and what should the borrower do about it?

The aforementioned transaction is impermissible. The excuse you provided does not absolve you from asking. You should inquire with trustworthy scholars about the permissibility of what you intend to undertake. As for the project itself, there is no impediment to working on it and benefiting from it.