Can I backup using cellular data instead of wifi

Sorry, not with an iPhone 7. See the following from Back up iPhone - Apple Support (ZA)

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.

If you have a MiFi or JetPack or analogous device from your carrier, yes. Otherwise, not on an iPhone 7.