It wasn't suppressed. Scholars have extensively studied it and dated it, and dismissed it as a late medieval or early Renaissance forgery. You can find a ton of information just by googling, or if you have access to an academic library, you can read reams of peer-reviewed papers by historians and textual analysts who specialize in New Testament studies. You won't find a single qualified scholar who asserts that the Gospel of Barnabas is the real deal.

And of course, if it were the real deal, a scholar going out on a limb and demonstrating it would make their career. So it's not like scholars lack motivation to authenticate Barnabas.

It's just that nobody has been able to, because it's not authentic.