An unknown error occurred iCloud backup

Hi Metalsmile,

We'd love to help resolve the issue you're having backing up to iCloud. Let's follow the steps below to troubleshoot, and that should take care of it for you.

"If an alert says that there's not enough iCloud storage

1. In iOS or iPadOS, go to Settings > [your name].
2. Tap iCloud. At the top, you can check how much iCloud storage you've used.
3. Tap Manage Account Storage or Manage Storage.
4. Tap Backups, then tap the device you're using. Under Last Backup and Backup Size, you can check Next Backup Size. It may take a few minutes for your device to calculate Next Backup Size. 
5. If your backup needs more space than the amount you have available in iCloud, you can: 

• Delete information that you don't need to reduce the size of your backup
• Upgrade your iCloud+ plan to get more space

If you still need help, contact Apple Support.

If a message says that your last backup couldn't be completed

1. In iOS or iPadOS, go to Settings > Wi-Fi. Check that you're connected to Wi-Fi. 
2. Go to Settings > General, then tap Software Update. Download and install any available updates for your device. 
3. Try to back up on another Wi-Fi network.
4. Check to make sure that you have enough iCloud storage for the backup. 
5. If you still need help, contact Apple Support.

If your iCloud backup is taking longer than expected to complete

1. In iOS or iPadOS, go to Settings > Wi-Fi. Check that you're connected to Wi-Fi. 
2. Check your upload speed.
3. Leave your device connected to power and Wi-Fi for 24 hours. If your backup still isn't done, archive important data then contact Apple Support. 

If the iCloud Backup option is greyed out

1. Check if a restore is still in progress. Go to Settings > [your name] > iCloud > iCloud Backup. If your device is still being restored, you see “This [device] is currently being restored and will automatically back up when it is done.” You can create a new backup after your device finishes restoring.
2. Check whether you installed a profile that restricts iCloud Backup. Go to Settings > General > VPN & Device Management to see a list of installed profiles."

Reference: If you can't back up to iCloud - Apple Support

Cheers!