My copy of Flight Sim just won't update, it's stuck in a weird loop and won't do anything. Out of 53 hours "playtime" I've actually played it for less than 2 hours.
If you have anything in your Community folder, move it out to another folder somewhere else, re-run the game, and then it should work. Once it's updated, you can move it back and it'll still work.
If not, there are plenty of guides online as this is a fairly common problem. For me, moving the Community folder always worked.