Pope Pius VI reigned as Pope from 1775 to 1799 meaning that the entire American Revolution occurred in his term of Papacy. When I googled this very same question, all I could find was him condemning the French Revolution, not the American one. Can anyone who studies the history of the Papal position or someone who studies the American Revolution and has in depth knowledge of how the world viewed tell me what Pope Pius VI thought of it?
Here's an older answer for you:
https://www.reddit.com/r/AskHistorians/comments/1ta0ef/was_there_a_papal_reaction_to_the_american/