How can I backup without a Wi-Fi

You can backup by connecting it to a computer no Wi-Fi needed for that. Choose the Backup with your Mac or Backup with your PC sections in the support document you posted from, or click below:

Back up with your Mac

Back up with your PC

If you have an iPhone 12 or 13 connected to 5G cellular service ands the carrier supports it, you can backup to iCloud over cellular.

Back up to a Mac or a PC that has iTunes installed on the device using a USB to Lightning cable. Details in the link below:

How to back up your iPhone, iPad, and iPod touch - Apple Support

Please use iTunes on a computer.