How to Turn On or Off Microsoft Defender Antivirus in Windows 10  

Poccapx said:

DisableAntiSpyware is no longer a way to turn off Windows Defender.

Microsoft has just recently confirmed on their website that "DisableAntiSpyware is discontinued and will be ignored on client devices, as of the August 2020 (version 4.18.2007.8) update to Microsoft Defender Antivirus."
Source: https://docs.microsoft.com/en-us/win...bleantispyware

Looks like Tamper Protection wasn't the issue after all. Microsoft has recoded Microsoft Defender to ignore this registry key.

Meaning that there is currently no official way to turn Defender off without falling to third party AV (which uses some publicly undisclosed mechanisms to turn Defender off). Is it possible to revert to a version prior to this 4.18.2007.8, lock it there (by changing folder ownership rights, for instance) and still retain definition updates from MS? While we wait for some workaround for this.

But how? In services anything for WinDefend, WdNisSvc and WdFilter is greyed out, while net stop states that Access is denied.

Unfortunately on LTSC, TP doesn’t seem to be disengageable:

Poccapx said:

Using LTSC 1809, so there’s no status in Security. However, MpComputerStatus in PowerShell, as stated, reports IsTamperProtected: False.

Which entries in the registry do you refer to?

News on the topic:
Microsoft makes it difficult to disable Windows Defender on Windows 10