Split tunneling sends selected traffic through a VPN while other traffic uses a different route. The selection may be based on an app, destination or other rule supported by the VPN software.
An everyday example
You might route ordinary browsing through a VPN while allowing a local service to use its normal connection. That can be convenient, but it means a single IP check cannot describe all traffic from the device.
There are two common ways to express a rule: include only selected apps, or exclude selected apps. Read the actual setting carefully. Choosing the wrong interpretation can produce the opposite of your intended routing.
How to check a rule
Write down which app should use the VPN and which should not. Test each app separately. A browser showing the VPN address supports a conclusion about that browser request; it does not establish the route used by an excluded game or background service.
If the rule concerns a specific destination, test that destination. An unrelated IP lookup may be outside the rule you are trying to verify. Keep DNS and IPv6 behavior in view as well.
Where to look for support
Provider implementations differ. The cited Proton guide is an example of how one provider documents this feature. It is not evidence that Zenshield exposes the same controls or supports the same platforms.
If your app offers no documented split-tunnel control, do not assume one exists. Use the working-VPN checks and ask support about the exact app and task you need to route.