Can’t finish iCloud backup

Try force restarting your phone and then try again.

Force restart iPhone X and later, iPhone 8, or iPhone 8 Plus:

1. Press and release the volume up button.
2. Press and release the volume down button.
3. Press and hold the side button.
4. When the Apple logo appears, release the button.

We can't fix a problem with your WiFi network.

Your statement begs the question, have you tried using another WiFi network?