How to count collections in Firebase SwiftUI

I would like to get a count of items within the collection e.g. total number of images saved by users, so that I can display them in the app’s home page. I have found this documentation from Firebase’s website https://firebase.google.com/docs/firestore/query-data/aggregation-queries. However, when I try to implement the code, I been getting a couple of error.

let query = db.collection("cities").whereField("state", isEqualTo: "CA")
let countQuery = query.count
do {
    let snapshot = try await countQuery.getAggregation(source: .server)
    print(snapshot.count)
} catch {
    print(error);
}

Here are the errors I get. I have imported Firebase, FirebaseFirestoreSwift in the file.

I have try googling and searching for how to get data, but I could not find anything close from the internet. More specifically for SwiftI. Hope you guys can help me. Would appreciate your help.