iOS 14 widget works locally, but fails via TestFlight

Make sure that you use Xcode 12 beta 4 and iOS 14 beta 4 on your devices.

Make sure that you have placeholder(in:) implemented. Make sure that you don't have placeholder(with:) because that's what the previous beta of Xcode was suggesting with autocompletion and without that you won't get your placeholder working. I think this whole problem is caused by the WidgetKit methods getting renamed but that's another story.

As per the release notes, you need to set "Dead Code Stripping" to NO in your extension target's build settings. This is only necessary for the extension's target.

When uploading your archive to the App Store Connect, uncheck "Include bitcode for iOS content".

Delete your old build from a device when installing a new beta.

Code Block 
import WidgetKit
import SwiftUI
import CloudKit
struct WidgetCloudKit {
    static var gameLevel: Int = 0
    static var gameScore: String = ""
}
struct Provider: TimelineProvider {
    private var container = CKContainer(identifier: "MyIdentifier")
    static var hasFetchedGameStatus: Bool = false
    
    func placeholder(in context: Context) -> SimpleEntry {
        return SimpleEntry(date: Date(), gameLevel: 0, gameScore: "0")
    }
    
    func getSnapshot(in context: Context, completion: @escaping (SimpleEntry) -> ()) {
        let entry: SimpleEntry
        if context.isPreview && !Provider.hasFetchedGameStatus {
            entry = SimpleEntry(date: Date(), gameLevel: 0, gameScore: "0")
        } else {
            entry = SimpleEntry(date: Date(), gameLevel: WidgetCloudKit.gameLevel, gameScore: WidgetCloudKit.gameScore)
        }
        completion(entry)
    }
    func getTimeline(in context: Context, completion: @escaping (Timeline<Entry>) -> ()) {
            let pred = NSPredicate(value: true)
            let sort = NSSortDescriptor(key: "creationDate", ascending: false)
            let q = CKQuery(recordType: "gameData", predicate: pred)
            q.sortDescriptors = [sort]
            let operation = CKQueryOperation(query: q)
            operation.desiredKeys = ["level", "score"]
            operation.resultsLimit = 1
            operation.recordFetchedBlock = { record in
                DispatchQueue.main.async {
                    WidgetCloudKit.gameLevel = record.value(forKey: "level") as? Int ?? 0
                    WidgetCloudKit.gameScore = String(record.value(forKey: "score") as? Int ?? 0)
                    Provider.hasFetchedGameStatus = true
                    var entries: [SimpleEntry] = []
                    let date = Date()
                    let entry = SimpleEntry(date: date, gameLevel: WidgetCloudKit.gameLevel, gameScore: WidgetCloudKit.gameScore)
                    entries.append(entry)
                    let nextUpdateDate = Calendar.current.date(byAdding: .minute, value: 15, to: date)!
                    let timeline = Timeline(entries: entries, policy: .after(nextUpdateDate))
                    completion(timeline)
                }
            }
            operation.queryCompletionBlock = { (cursor, error) in
                DispatchQueue.main.async {
                    if let error = error {
                        print("queryCompletion error: \(error)")
                    } else {
                        if let cursor = cursor {
                            print("cursor: \(cursor)")
                        }
                    }
                }
            }
                    
            self.container.publicCloudDatabase.add(operation)
    }
    
}
struct SimpleEntry: TimelineEntry {
    var date: Date
    var gameLevel: Int
    var gameScore: String
}
struct WidgetEntryView : View {
    var entry: Provider.Entry
    
    var body: some View {
        GeometryReader { geo in
            VStack {
                Image("widgetImage")
                    .resizable()
                    .aspectRatio(contentMode: .fit)
                    .frame(width: geo.size.width)
                HStack {
                    VStack {
                        Text("LEVEL")
                        Text(entry.gameLevel == 0 ? "-" : "\(entry.gameLevel)")
                    }
                    VStack {
                        Text("SCORE")
                        Text(entry.gameScore == "0" ? "-" : entry.gameScore)
                    }
                }
            }
                .unredacted()
        }
    }
}
@main
struct Widget: SwiftUI.Widget { 
    let kind: String = "MyWidget"
    
    var body: some WidgetConfiguration {
        StaticConfiguration(kind: kind, provider: Provider()) { entry in
            WidgetEntryView(entry: entry)
        }
        .configurationDisplayName("Game Status")
        .description("Shows an overview of your game status")
        .supportedFamilies([.systemSmall])
    }
}