So intercept whatever mechanism it's using to detect SIP enabled status...?

You would have to somehow compromise the security coprocessors, even on Android where more of the system is open source, Play Integrity relying on this has killed pretty much all methods of tricking application code that the system is stock outside of downgrade attacks (by convincing the application the phone doesn't support newer verification methods).

We can run tasks on them that only produces valid output if the boot chains is verified.

If Apple launches an attestation API that has key material that they control on the hardware co-processor that it authenticates with Apple servers and passes the result back to the game server, then there's no mechanism to intercept it.