I have had this happen to me once or twice over the years. You go to install a new version iOS or iPadOS and you get the messages, “Software Update Failed”. That is very disconcerting to say the least. I hope this never happens to you, but for future reference this article describes several things you can to fix this problem. Obviously, If you don’t fix this issue, no more updates, so it would behoove you to read this article or at least bookmark it for possible future needs.