Does File History backup all things on my PC?

It backs up all files not the os files.

MS does not know how to make backup apps.  Please learn from Mac Time machine!

If you’re looking to create a complete backup of your system, including Windows itself, applications, and settings, you might want to consider using Windows Backup and Restore or a third-party backup solution. 

I'm a major fan of simply copying all my files to a backup drive. Then you have complete control over what files are back up and restored. You aren't subject the the whims of a backup app. I use robocopy from the command line. But using File Explorer is a fine choice.

I suggest to use Windows Backup app included with Windows 11 to backup your data. It can backup files, apps, credentials and settings.

File History automatically backs up files that are in your libraries, contacts, favorites, Microsoft SkyDrive and on your desktop. If the originals are lost, damaged, or deleted, you can restore all of them. You can also find different versions of your files from a specific point in time. Over time, you'll have a complete history of your files.

If you just wanna backup files in your user folder，File History is a good choice,but it‘s not the best for protecting the system along with your files