You can block internet access to apps in Windows 11 by configuring Windows Defender Firewall settings.
To block internet access, open Windows Defender Firewall, go to Advanced Settings, select Outbound Rules, and create a new rule.
To disable the firewall rule blocking apps from accessing the internet, go to Advanced Settings, select Outbound Rules, find the rule, and disable or delete it.
Alternatively, you can use TinyWall, a firewall program, to block internet access to apps on Windows 11 by managing application exceptions.