perhaps this is one good reason why you should stick to running Win10 instead of upgrading to Win11, chillgates
edit 9/10: aww crap, the problem is also occurring recently for some Win10 users where Defender Control can't disable Windows Defender, maybe because of installing/updating to the newest Defender antimalware platform update (v4.18.2108.7)
fortunately I have not updated that to v4.18.2108.7 and still have the older v4.18.2107.4 antimalware client for Windows Defender from last month
edit 9/10: aww crap, the problem is also occurring recently for some Win10 users where Defender Control can't disable Windows Defender, maybe because of installing/updating to the newest Defender antimalware platform update (v4.18.2108.7)
fortunately I have not updated that to v4.18.2108.7 and still have the older v4.18.2107.4 antimalware client for Windows Defender from last month