It looks to me like FirebaseFirestoreSwift cannot be installed using the Swift Package Manager because FirebaseFirestoreSwift is still in beta.
I understand that FirebaseFirestoreSwift could be installed using Cocoapods but I don't want to use cocoapods because I believe (perhaps incorrectly) that source control using github with cocoapods can be challenging.
I want FirebaseFirestoreSwift because I believe that is the only way to get the SwiftUI codable protocol working with Firebase.