This is a FileManager extension that helps you find the documents directory of the user, decode data saved in documents and save data to documents, and bellow there's a file on how to use it.

FileManagerDecodableExtension.swift

import Foundation

extension FileManager {
    static var documentsDirectory: URL {
        URL.documentsDirectory
    }
    
    func decode<T: Codable>(from url: URL) throws -> T {
        let data = try Data(contentsOf: url)
        
        let decoder = JSONDecoder()
        let decoded = try decoder.decode(T.self, from: data)
        return decoded
    }
    
    func save<T:Codable>(items: T, to url: URL) {
        do {
            let data = try JSONEncoder().encode(items)
            // .atomic means that it's going to write everything at once, this should always be used.
            // We use .completeFileProteccion if we want the data to be write with encryption, so the data will be available just if the user is already authenticated. 
            try data.write(to: url, options: [.atomic, .completeFileProtection])
        } catch {
            print("Error saving data to url: \(error.localizedDescription)")
        }
    }
    
    func deleteItem(at url: URL) {
        do {
            try FileManager.default.removeItem(at: url)
        } catch  {
            print("[😕] Couldn't delete file from url: \(url)!")
        }
    }
    
    /// Delete all files older than a specified number of days from a specified directory url
    /// - Parameters:
    ///   - url: The URL directory
    ///   - olderThan: A number of days as an integer
    func deleteFilesFromDirectory(_ url: URL, olderThan: Int) {
        guard FileManager.default.fileExists(atPath: url.path) else { return }
        
        do {
            let fileNames = try FileManager.default.contentsOfDirectory(atPath: url.path)
            for fileName in fileNames {
                let path = url.appendingPathComponent(fileName).path
                let attributes = try FileManager.default.attributesOfItem(atPath: path)
                if
                    let creationDate = attributes[.creationDate] as? Date,
                    creationDate < Calendar.current.date(byAdding: .day, value: olderThan, to: .now) ?? .now {
                    
                    try FileManager.default.removeItem(atPath: path)
                }
            }
        } catch {
            print("[😕] Error trying to delete all files older than \(olderThan) days from: \(url.path), Error: \(error.localizedDescription)")
        }
    }
}

ViewModel.swift

import Foundation

// MARK: HOW TO USE IT
struct Card: Codable, Identifiable {
    var id = UUID()
    let prompt: String
    let answer: String
}

class ViewModel: ObservableObject {
  @Published var cards: [Card]
  
  let savePath = FileManager.documentsDirectory.appending(path: "Cards")
  
  init() {
      do {
          cards = try FileManager.default.decode(from: savePath)
      } catch {
          print("Error getting data from url: \(error.localizedDescription)")
          cards = []
      }   
   }
  
   private func saveData() {
       FileManager.default.save(cards, to: savePath)
   }
}