The docs (https://www.pulumi.com/docs/reference/pkg/nodejs/pulumi/gcp/dns/#RecordSet) show this code with

accessConfig.0.natIp

. Is this valid TS?

const frontendRecordSet = new gcp.dns.RecordSet("frontend", {
    managedZone: prod.name,
    rrdatas: [frontendInstance.networkInterfaces[0].accessConfig.0.natIp],
    ttl: 300,
    type: "A",
});

No - that looks like a bug in the docs. Could you open an issue to track?