It can’t be used with ProtonVPN (I assume) but I use NoRoot Firewall for exactly this purpose. It works by setting up a VPN and letting you enable / disable network access for each app, including system apps. It can also block on just WiFi or just cell data or both or neither. It blocks all apps by default until you configure their access. You can also setup more advanced rules for all apps or just some apps. For instance, you can set it where an app can contact AppCompany.com but not Google.com
You could improve this by comparing it to someone beheading a statue of Jesus at the state capitol. I don’t know if that has happened, but it would be more likely to elicit the response you describe.