If I wanted to: How do I lockdown the network on the computer.

I was just wondering, has Microsoft implemented a way to lockdown the internet access on Windows Defender (Security) yet? I did awhile ago place such a request on the Feedback Hub but had no response yet from the development team at Microsoft. Is such a feature possible with Windows Security at the moment? Or will we still have to use third-party internet security software's for the time being.

You can use Windows Firewall to block Internet access. Do so by introducing new Outbound Rules.

I believe all 3rd-party security software with similar functions have to go through the Windows Firewall. They just show you different GUIs to make the job more user-friendly.

You can stop internet access by removing the default gateway

I disable the network adapter or turn off the router.