Javascript retry function

I am writing a mobile application using React Native and Firebase on the server-side. After registering, the client must wait for a Firebase function to create a Firestore document. I've made a retry function based on this blog. My only problem is that it gives me the error "Nothing was returned from render. This usually means a return statement is missing. Or, to render nothing, return null". I know what this error means, but I could not find the source of the problem. I've probably overlooked something but I would appreciate it if someone could help me find it. This is my render method:

render() {
    const { currentUser } = this.props

    const retry = async (fn, maxAttempts) => {
        const execute = async (attempt) => {
            try {
                return await fn()
            } catch (err) {
                if (attempt <= maxAttempts) {
                    const nextAttempt = attempt + 1
                    console.log(`Retrying after 1 second due to:`, err)
                    return delay(() => execute(nextAttempt), 1000)
                }
            }
        }
        return execute(1)
    }

    const delay = (fn, ms) => new Promise((resolve) => setTimeout(() => resolve(fn()), ms))

    const app = () => {
        return (
            <Tab.Navigator
                <Tab.Screen name="Feed" component={FeedScreen} options={{
                    headerRight: () => (
                        <Button
                            onPress={() => console.log("Filter Function")}
                            title="Filters"
                        />
                    ),
                }} />
                <Tab.Screen name="Search" component={SearchScreen} options={{ headerShown: true }} />
                <Tab.Screen name="Create Post" component={CreatePostScreen} options={{ unmountOnBlur: true }} />
                <Tab.Screen name="Messages" component={MessagesScreen} />
                <Tab.Screen name="Profile" component={ProfileScreen} options={{
                    headerRight: () => (
                        <Button
                            onPress={() => RootNavigation.navigate("Settings")}
                            title="Settings"
                        />
                    ),
                    title: currentUser.displayName
                }} />
            </Tab.Navigator>
        )
    }

    retry(app, 60)
}