At theend of last year, Google One added a VPN on higher-tier plans to help build out the subscription offering. Still only available on Android, the Google One app is working on the ability to “block internet if VPN disconnects.”
Update: The “Block internet if VPN disconnects” preference is live, but oddly placed in Google One’s “Settings” tab rather than the dedicated page under “Advanced VPN settings.”
If your device is restarted, the VPN will try to reconnect automatically. Before it reconnects, your internet connection won’t be blocked or protected.
Meanwhile, system Settings does not recognize this app-level capability as an “Always-on VPN,” with “Block connections without VPN” not controllable from there.
