Can you do your iCloud backup without using Wi-Fi
Can I do my iCloud back up without being connected to Wi-Fi?
iPhone 11 Pro Max, iOS 15
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Yes, in some cases. See the following from Back up iPhone - Apple Support
Note: On models that support 5G, your carrier may give you the option to back up iPhone using your cellular network. Go to Settings > [your name] > iCloud > iCloud Backup, then turn on or off Backup Over Cellular.