If you can't find any utility at Windows Defender, the free Microsoft antivirus installed and automatically enabled with Windows 10, then read this article.
This article is the upgrade of the previous one but for Windows 10 Fall Creators Update.
To do this, open with the help of Cortana/Research Bar, the local group strategy editor by typing gpedit.msc.
From the tree of the left column, unfold the following:
Computer Configuration \ Administration Templates \ Windows Components \ Windows Antivirus Windows Defender
In the right column, double-click on Disable Windows Defender antivirus.
Check the option Activated then do OK.
Windows Defender is now disabled, so the icon of the latter in the Taskbar displays a red cross.
To reactivate Windows Defender, open this one, and click the button Restart now.
You will notice in the capture the display bug indicating “Your device is protected” while the real-time protection is turned off.
English (UK)
thanks c nickel