I use Marcel Bokhorst's excellent Netguard app (<a href="https://www.netguard.me/" rel="nofollow">https://www.netguard.me/</a>) on unrooted Android devices as a firewall and have it set to "deny" as a default, so no newly installed app gets network access. If an app does not work in this "offline mode" I inspect what it's trying to do as Netguard maintains a log which one can even export in PCAP format for further processing if needed.<p>BTW, even my wife and other family members, all classical end users, can easily handle Netguard after a short introduction.