Firestore: Unsupported field value: a custom Timestamp object after updating firebase version

I updated to firebase v11.3.1 from v8.2.5 and I am using the compat mode.

However my updates no longer work due to using FieldValue.serverTimestamp() for a date field.

Any suggestions on how to resolve this?

Error

FirebaseError: Function DocumentReference.update() called with invalid data. Unsupported field value: a custom Timestamp object (found in field dateModified in document...


Code

constructor(private db: AngularFirestore)

return this.db.collection(this.membersCollectionPath).doc(uid)
.update({ ...changes, dateModified: getTimestamp() });

---
import { AngularFirestoreDocument } from '@angular/fire/compat/firestore';
import firebase from 'firebase/compat/app';
import 'firebase/compat/auth';
import 'firebase/compat/firestore';

export function getTimestamp() {
return firebase.firestore.FieldValue.serverTimestamp();
}


I also tried the below with the same error:

export function getTimestamp() {
return firebase.firestore.Timestamp.fromDate(new Date());
}

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