App Inventor does not have a VpnService component. It has the WebViewer. Other developers use the WebViewer in their GooglePlay apps. What other code do you have in your app that might be triggering Google sending you the notice? The community has no record of another developer receiving this notice. What is different with your app since you seem to be the only App Inventor developer receiving this message? You could ignore the advice or specifically contact Google and ask them what your app does (or does not do) that elicited the notice you received.
Perhaps: