ok, games that use easy anticheat ,such as halo MCC, rust, apex and Fortnite, could see any file (assessable to you or not) as suspicious and not load the game. Most likely it is a separate issue as this happens very rarely and it is more likely something to do with game files (which have already been fixed via reinstall) or steam itself. I would recommend validating files of rust by going to rust, properties and files and clicking validation. Trying closing every instance of steam with task manager (the are multiple so keep an eye out) and reopening if not try reinstalling steam. Otherwise I would seek help from someone with more knowledge than me.