iCloud backup on SE.

Hi,

Here what I found for you:

If the iCloud Backup option is greyed out

1. Check if a restore is already in progress. 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 > Device Management to see a list of installed profiles. 

Full article here.

Hi,

Follow instructions on this page.