interface MyV10ServerType {
  indexed: {
    [name: string]: {
      booleanProperty: boolean,
      numberProperty: number
    }
  }
};

const update: UpdateData<MyV10ServerType> = {
  'indexed.foo.booleanProperty': true <-- TS2322: Type 'true' is not assignable to type '{ booleanProperty?: boolean | FieldValue | undefined; numberProperty?: number | FieldValue | undefined; } | FieldValue | undefined'.
}

updateDoc<MyV10ServerType>(docRef, update);

const update: UpdateData<MyV10ServerType> = {
  'indexed.foo.booleanProperty': true
}

updateDoc<MyV10ServerType>(docRef, update);

const update: UpdateData<MyV10ServerType> = {
  'indexed.foo': 'foo is not a string, it should be an object, but we can't enforce that...'
}

// This is an example of update data that does a full object replacement
const update: UpdateData<MyV10ServerType> = {
  indexed: {
    foo: {
      booleanProperty: true,
      numberProperty: 1
    }
  }
}

interface NestedObject {
  indexed: {
    // see, no index signature on this line
    foo: {
      booleanProperty: boolean,
      numberProperty: number
    }
  }
};

const update: UpdateData<NestedObject> = {
  'indexed.foo.booleanProperty': true // we have type safety and auto-complete for this
}