You can’t block windows system files else windows will not run so get that idea out of your head. You should be more careful not to get viruses and malware in the first place. Do a clean install and change your online habits to good safe ones
Trying to block Cmd is ridiculous. If you could block it windows wouldn’t even run properly
Also you don’t need bit defender or any other crap like that Windows defender is good enough don’t be fooled by what people say around here most antivirus programs stank and cause huge performance problems
Windows defender is built-in and windows firewall is already built-in and your best protection is what resides between your ears