One of the pain points in migrating from one Android smartphone to another is the fact that you are unlikely to land in the same device state as you started off, in the context of your app data. The problem is even more prominent when you migrate across different OEMs, as specific OEM solutions are often centered towards that ecosystem. Google attempted to take a crack at this problem by leveraging the Google Play Services framework and Google Drive to provide a built-in backup manager service for Google's Android. This built-in solution backs up contacts, call history, text messages, and certain application data and device settings to Google Drive automatically, but starting from Android Pie, you can also trigger a backup yourself. However, users have been complaining that backups to Google Drive have been broken for the past several months.
According to AndroidPolice, several users have been complaining over the months about how Google Drive backups have been entirely broken for them. The "Back up now" button is greyed out and cannot be clicked, and the phone stops backing up data without any warnings. This issue has been spotted across a wide variety of devices and other variables, so you may want to check if your device has been backing up data or not.
Sadly, Google has not yet acknowledged the issue, meaning that there is no official solution to the bug. Thankfully, you can take matters in your hand and force a backup through a few simple ADB commands. As mentioned by XDA Senior Member Dexer125 in his thread, you can force a backup to occur using the shell command interface for the backup manager:
adb shell
bmgr run
bmgr backupnow --all
This should force a backup on your device. If you get "Backup finished with result: Backup Cancelled", then run the following commands:
bmgr backupnow appdata
bmgr backupnow --all
This should hopefully return a successful result. Once it is done, reboot your device. The "Back up now" button should now be clickable and your data should be getting backed up in the background. However, we still hope that Google acknowledges the issue and rolls out a fix.
Guide to fix Google Drive "Waiting to Backup" bug -- XDA Thread
While this issue is certainly a problem for the users it affects, Google also should recognize the fact that the app and device setting backup situation on Android is very poor compared to the robust solution that Apple offers for its devices. Granted, Apple deals with a significantly smaller pool of devices, and the diversity in the Android ecosystem is absolutely huge.
App data restoration was introduced back in Android 6.0 Marshmallow as "Auto Backup for Apps".
Auto Backup for Apps automatically backs up a user's data from apps that target and run on Android 6.0 (API level 23) or later. Android preserves app data by uploading it to the user's Google Drive—where it's protected by the user's Google Account credentials. The amount of data is limited to 25MB per user of your app and there's no charge for storing backup data. Your app can customize the backup process or opt out by disabling backups.
By default, apps are opted-in to having up to 25MB of their (eligible) data backed up to the user's Google Drive account. But for various reasons, many developers opt-out of having their apps' data saved to Google Drive.
As for device settings, Google Drive backups include the values in Settings.System, Settings.Global, and Settings.Secure. But since these Settings tables tend to differ for each OEM, a lot of the data does not get successfully backed up or restored.
Because of these reasons -- app developers opting out, and variances in OEM implementations -- Android's backup and restore has felt frail and incomplete. Most users are unlikely to know about the pain point until they reach the junction of having their data restored -- only to find that they have to spend a lot of time getting their new phone to resemble the software state of their older one. Perhaps its time for Google to put its foot down in some of these areas?