My Backup now is greyed out and my iPhone hasn’t backed up in 4 months. How can this be fixed?

See -> If you can't back up to iCloud -> If you can't back up to iCloud - Apple Support

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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. 

Get support from Apple directly -> Get Support or call Apple in your region see -> Contact Apple for support and service