Sorry for doing this. I did it to boost my post and get responses, as it was a bit urgent. It won't happen again. I already have your answer. Thanks for your suggestion.

Yes, it loads sysex (asks for system extension permission to load). Yes, NE provider is instantiated (asks for network extension permission). We are saving VPN configurations using saveToPreferences method of NETunnelProviderManager and connecting to VPN using startTunnel method of NETunnelProviderSession. Since SIP is enabled, it is difficult to debug. But I checked by adding logs and it is like it fails in startTunnel method.

Anyway, if there is any error with the code, it should also fail in case SIP is disabled. But it works in case SIP is disabled and it does not work with SIP enabled. So, should there be any error with the code or configuration or notarization? Even if SIP is enabled or disabled, it works fine on macOS 13.* and 14.*. But in the case of macOS 15.1, it works if SIP is disabled and not if SIP is enabled. macOS 15.0 did not work in either case.

Thank you for your reply on this. Sorry for delaying reply from my side. I found the actual cause and I have fixed it. It was very minor human mistake where I was making mistake while notarization.