What backs the U.S. dollar?

I'm curious to understand what backs the value of the U.S. dollar. As the world's reserve currency, it's a widely used and trusted form of payment. But what exactly gives it its strength and stability? Is it backed by gold, like it was in the past, or is there something else at play? And in today's digital age, with the rise of cryptocurrencies, how does the U.S. dollar maintain its status as the global standard for currency?