There is two of every System Folder in the side bar of File Explorer.

I don't know what happened to it it just started today.

Don't know how it happened, but you can fix it by copying & pasting this bit of code into an Administrative PowerShell window (WinKey+X):

Code:

$key = 'HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\FolderDescriptions'
gci $key |
   ?{(gp "$($_.PSPath)\PropertyBag" -ErrorAction SilentlyContinue).ThisPCPOlicy} | 
     ?{(gp $_.PSPath).Name -match '^Downloads|my |Personal'} |
         %{($_.OpenSubKey('PropertyBag', $True)).SetValue('ThisPCPolicy', 'Hide')}

Keith