With the release of Big Sur - Network Kernel extensions are now officially inaccessible. However I cannot find the equivalent functionality I need in the new Network Extensions API.
In my NKE (network kernel extension) - i was able to control the routing of packets in a specific application by hooking socket binds and/or rewriting the source IP of outgoing packets for that application. Doing this i could control which interface those packets went through for that application (so called split tunneling).
I cannot see how to do something similar to this with the new APIs. Do the new APIs provide for this use-case? is it possible?