Вы можете получить сгенерированный iceCandidate, установив событие peerConnection.onicecandidate.
(async () => {
const pc = new RTCPeerConnection();
pc.onicecandidate = evt => {
console.log(evt.candidate?.candidate);
};
const stream = await navigator.mediaDevices.getUserMedia({video:true});
stream.getTracks().forEach(track => pc.addTrack(track, stream));
const offer = await pc.createOffer();
await pc.setLocalDescription(offer);
})();