- Exit Steam on your PC. To do so, click Steam > Exit. You don’t want Steam running in your system tray while you do this.

- Create a backup profile in SyncBack where the Source directory is C:\Program Files (x86)\Steam (this is the default location, you may have installed it elsewhere)

Set your Destination as appropriate

- You only need to backup the sub-folders steamapps, userdata and the file steam.exe

- Run the profile

If you restore from the backup, when your run the restored steam.exe then it will self-repair. If a game supports Steam Cloud, Steam will re-download its save games.