Hi, does FBackup start with windows or only after someone interactively logs in?
No, that is not possible.
You did not understand the meaning of that option.
The "Run at Windows startup" will start FBackup after you log in to your Windows user account.
In order to run a scheduled backup, you need to be logged in.
If you want to run scheduled backups even if no user is logged in, please consider trying a commercial application as Backup4all.