As mentioned, the 1970s revival created a mix of history and modern invention, but there's something the others didn't highlight: a lot of the "authentic traditions" you see on social media and in tourist videos have basically been reconstructed from scratch. The original Venetian masks had very different rules from today's - for example, the Volto (that smooth white one) really did serve to hide identity, but it was used during specific periods, not year-round like it seems now. And those elaborate, colorful costumes you see in photos? Those are often recent creations by contemporary artisans who draw inspiration from the era, not exact replicas.
What's stayed authentic is more the concept than the form. The idea that Carnival was a moment of social freedom where you could be anyone thanks to the mask - that has real roots in past centuries. But here's the thing: the historically "authentic" Carnival lasted for weeks and had a completely different role in Venetian society; it was a genuine popular festival, not a spectacle for tourists like now. If you're looking for traditions that actually stay alive, focus more on the cultural meaning (the mask as freedom, controlled chaos, inversion of social roles) rather than the specific costumes you see in the squares.
Anyway, one genuine thing does remain: the artisans who make the masks still follow ancient techniques in papier-mâché craftsmanship and decoration. That one has carried on pretty much intact.