This is the most common report we get, and the instinct — reinstall the app — is almost always the wrong first move. Here is the order that actually narrows it down.
1. Try a different node in the same profile.
Do this before anything else. If another node works, the app, the profile and your permissions are all fine and you have a dead endpoint. That one step resolves the majority of these.
2. Check whether it is DNS.
If raw addresses work and names do not, the tunnel is up and name resolution is not. Switching the remote resolver is the quick test.
3. Check the protocol against your network.
UDP-based protocols such as Hysteria 2 are reachable on some networks and not others. A node that works on Wi-Fi but not on cellular — or the reverse — is usually this rather than a fault.
4. Only then look at the app.
On the macOS DMG build, confirm the system extension approval (separate thread). On Android, check battery optimisation if the tunnel dies when the screen is off.
What does not help
Reinstalling. Switching every setting at once — then you cannot tell which one mattered. Opening inbound ports in a firewall; nothing here needs them.
Longer write-up: VPN connected but no internet