I suspect you would enjoy the story of Furbeowulf.
http://www.trygve.com/furbeowulf.html
That page is old enough that it doesn’t seem to support HTTPS. If your browser automatically converts HTTP to HTTPS, you’re going to get a warning about an insecure connection. Here’s a wayback machine link that supports a secure connection:
https://web.archive.org/web/20230503215715/http://www.trygve.com/furbeowulf.html
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
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Edited with explanation and alternate link.