我有同样的问题，为什么丰富的通知不工作..和问题是与FCM mutable-content有效负载..它变成gcm.notification.mutable-content时，有效负载接收，这就是为什么有一个问题尚未解决。
有关详细信息，您可以查看此issue from github.
现在问题解决了。您可以检查该链接，也可以检查此answer AL。

只是更新了@ElCaptainv2.0的答案。
为FCM添加了mutable_content：
当前仅适用于iOS 10+设备。在iOS上，使用此字段表示APNS有效负载中的可变内容。发送通知且此字段设置为true时，可以使用Notification Service app extension在显示之前修改通知内容。对于Android和Web，将忽略此参数。
注意：参数值应为boolean，而不是Integer。
就在几个小时前，kroikie在GitHub thread中也提到了这一点。

我花了好几个小时，好几个小时，好几个小时，我所有的通知都运行良好，除了rich notification图像永远不会显示。下面是简单英语：
更改此内容：
"mutable-content": 1//错误
对此：
"mutable_content": true//正确
以下是传出的有效负载：

"aps": {
    "alert": {
        "title": "Hello",
        "body": "What do you think of this image?"
    },
    "mutable_content": true
},
"media-url": "https://firebasestorage.googleapis.com/....."

以下内容对我有效（2023年2月）
步骤1 -添加通知服务扩展
第2步-将目标添加到Podfile
步骤3 -使用扩展帮助程序
转换为Swift：

//
//  NotificationService.swift
//  RichNotification
//

import UserNotifications

class NotificationService: UNNotificationServiceExtension {
    var contentHandler: ((UNNotificationContent) -> Void)?
    var bestAttemptContent: UNMutableNotificationContent?
    
    override func didReceive(_ request: UNNotificationRequest, withContentHandler contentHandler: @escaping (UNNotificationContent) -> Void) {
        self.contentHandler = contentHandler
        bestAttemptContent = (request.content.mutableCopy() as? UNMutableNotificationContent)
        
        guard let bestAttemptContent = bestAttemptContent,
              let attachmentURLAsString = bestAttemptContent.userInfo["image"] as? String,
              let attachmentURL = URL(string: attachmentURLAsString) else {
            return
        }
        
        downloadImageFrom(url: attachmentURL) { (attachment) in
            if let attachment = attachment {
                bestAttemptContent.attachments = [attachment]
                contentHandler(bestAttemptContent)
            }
        }
    }

    override func serviceExtensionTimeWillExpire() {
        // Called just before the extension will be terminated by the system.
        // Use this as an opportunity to deliver your "best attempt" at modified content, otherwise the original push payload will be used.
        if let contentHandler = contentHandler, let bestAttemptContent =  bestAttemptContent {
            contentHandler(bestAttemptContent)
        }
    }
    
    private func downloadImageFrom(url: URL, with completionHandler: @escaping (UNNotificationAttachment?) -> Void) {
        let task = URLSession.shared.downloadTask(with: url) { (downloadedUrl, response, error) in
            // 1. Test URL and escape if URL not OK
            guard let downloadedUrl = downloadedUrl else {
                completionHandler (nil)
                return
            }
            // 2. Get current's user temporary directory path
            var urlPath = URL(fileURLWithPath: NSTemporaryDirectory ())
            // 3. Add proper ending to url path, in the case jpg (The system validates the content of attached files before scheduling the corresponding notification request. If an attached file is corrupted,
            let uniqueURLEnding = ProcessInfo.processInfo.globallyUniqueString + ".jpg"
            urlPath = urlPath.appendingPathComponent (uniqueURLEnding)
            // 4. Move downloadedUrl to newly created urlPath
            try? FileManager.default.moveItem(at: downloadedUrl, to: urlPath)
            // 5. Try adding getting the attachment and pass it to the completion handler
            do {
                let attachment = try UNNotificationAttachment (identifier: "picture", url: urlPath, options: nil)
                completionHandler(attachment)
            }
            catch {
                completionHandler(nil)
            }
        }
        task.resume()
    }
}

extension UNNotificationRequest {
    var attachment: UNNotificationAttachment? {
        guard let attachmentURL = content.userInfo["image"] as? String, let imageData = try? Data(contentsOf: URL(string: attachmentURL)!) else {
            return nil
        }
        return try? UNNotificationAttachment(data: imageData, options: nil)
    }
}

extension UNNotificationAttachment {
    convenience init(data: Data, options: [NSObject: AnyObject]?) throws {
        let fileManager = FileManager.default
        let temporaryFolderName = ProcessInfo.processInfo.globallyUniqueString
        let temporaryFolderURL = URL(fileURLWithPath: NSTemporaryDirectory()).appendingPathComponent(temporaryFolderName, isDirectory: true)

        try fileManager.createDirectory(at: temporaryFolderURL, withIntermediateDirectories: true, attributes: nil)
        let imageFileIdentifier = UUID().uuidString + ".jpg"
        let fileURL = temporaryFolderURL.appendingPathComponent(imageFileIdentifier)
        try data.write(to: fileURL)
        try self.init(identifier: imageFileIdentifier, url: fileURL, options: options)
    }
}

通过Firebase/FCM发送推送通知的cURL

curl --location --request POST 'https://fcm.googleapis.com/fcm/send' \
--header 'Authorization: key=<YOUR FCM KEY>' \
--header 'Content-Type: application/json' \
--data-raw '{
    "to": "fcm token for device or channel id",
    "content_available": true,
    "mutable_content": true,
    "notification": {
        "title": "Notification With Image",
        "mutable-content": true,
        "body": "Test Message "
    }, 
    "data": {
        "image": "https://upload.wikimedia.org/wikipedia/commons/1/16/HDRI_Sample_Scene_Balls_%28JPEG-HDR%29.jpg"
    }
}'