You can use the Microsoft Tunnel Monitor app to monitor the traffic on the VPN server. It is available for both Android and iOS devices. Here is the link to download the app:
- Microsoft Tunnel Monitor app on Google Play Store: https://play.google.com/store/apps/details?id=com.microsoft.intune.tunnelmonitor&hl=en_US&gl=US
- Microsoft Tunnel Monitor app on Apple App Store: https://apps.apple.com/us/app/microsoft-tunnel-monitor/id1549268129
Alternatively, you can also use the Microsoft Endpoint Manager admin center to view the VPN server traffic. Here is the link to the documentation on how to monitor VPN traffic using the admin center: