Disable Real time protection and all other protections in the Security Dashboard Settings.
Edit Group Policy to disable Windows Defender. Search "Group Policy" in the start menu and hit enter. Navigate to Computer configuration -> Windows Components -> Microsoft Defender Antivirus -> Double Click Turn off Microsoft Defender Antivirus and set to Enabled.
Download Autoruns from sysinternals and then reboot to safe mode (Google how to do that). After rebooting launch Autoruns and go to options and uncheck Hide Microsoft and Hide Windows Entries.
Disable everything related to Windows Defender in the Services tab, Scheduled Tasks tab and Drivers tab. Reboot and you should be done!
- Enable the group policy Turn off Enhanced Notifications in Computer configuration -> Windows Components -> Microsoft Defender Antivirus -> Reporting to stop getting annoying notifications.
- Disable Microsoft Smartscreen.