Xcode – SwiftUI Sign in with Apple button dark mode

At first add

@Environment(.colorScheme) var colorScheme

and then add the style depends of variable

.signInWithAppleButtonStyle(colorScheme == .dark ? .white : .black)

In your case, it would look like this:

import SwiftUI
import CryptoKit
import FirebaseAuth
import AuthenticationServices

struct SignInWithAppleButtonView: View {
    @Environment(.colorScheme) var colorScheme
    @State var currentNonce:String?

    var body: some View {
        SignInWithAppleButton(
            onRequest: { request in
                let nonce = randomNonceString()
                currentNonce = nonce
                request.requestedScopes = [.fullName, .email]
                request.nonce = sha256(nonce)
            },
            onCompletion: { result in
                switch result {
                case .success(let authResults):
                    switch authResults.credential {
                    case let appleIDCredential as ASAuthorizationAppleIDCredential:

                        guard let nonce = currentNonce else {
                            fatalError("Invalid state: A login callback was received, but no login request was sent.")
                        }
                        guard let appleIDToken = appleIDCredential.identityToken else {
                            fatalError("Invalid state: A login callback was received, but no login request was sent.")
                        }
                        guard let idTokenString = String(data: appleIDToken, encoding: .utf8) else {
                            print("Unable to serialize token string from data: (appleIDToken.debugDescription)")
                            return
                        }

                        let credential = OAuthProvider.credential(withProviderID: "apple.com",idToken: idTokenString,rawNonce: nonce)
                        Auth.auth().signIn(with: credential) { (authResult, error) in
                            if (error != nil) {
                                // Error. If error.code == .MissingOrInvalidNonce, make sure
                                // you're sending the SHA256-hashed nonce as a hex string with
                                // your request to Apple.
                                print(error?.localizedDescription as Any)
                                return
                            }
                            print("signed in")
                        }

                        print("(String(describing: Auth.auth().currentUser?.uid))")
                    default:
                        break

                    }
                default:
                    break
                }
            }
        )
        .signInWithAppleButtonStyle(colorScheme == .dark ? .white : .black)
    }
}