The United States of America is a collection of former colonies and territories that either revolted against imperial British rule or petitioned to join the union. Because the United States economic system is not the same as the government, and because people own private property and private capital rather than the government preponderantly (private capital is of far greater value today than public capital), answers to questions about when the American empire will collapse, like a souffle as it were, are challenging to answer as they are a little off the mark.
One might ask when the dollar will collapse and that would be possibly more accurate. Experts may know if it will yet the dollar is a universal floating currency held by global plutocrats and Chinese communists as well as Americans from the U.S.A., Mexico and Peru etc.
The American economic system’s wealthy people-plutocrats are part of a global community of plutocrats in my opinion, and wondering when their power will end is another interesting question different of course than the one about when the non-real American empire will end.
America was an empire for 20 years when it had the Philippines as a colony as a result of the Spanish American war, and so when the Philippines took their liberty from the U..S.A. I suppose that was the actual collapse of the American empire- in either 1935 or 1946 depending upon if one regards a commonwealth as independent.
One further could wonder if the influence of globalist plutocrats and corporations that are preponderantly American will collapse and that is a tough question. As an occasional science fiction writer I could develop innumerable scenarios for that, for instance, when artificial intelligence takes over the world, when a global pandemic crashes world population or when too much social use of dope and evil broadcast media reduces the intelligence of everyone so far that they cannot understand the complexity any more. It is sometimes fun to consider alternative dystopias and utopias as future possibilities too help realize the futility of every getting good intelligent politicians to make the world a much better place.