i just got iphone 17. Now while setting up it shows "No internet connection Apple Intelligence setup and activation are unavailable when your device is offline. Connect to the internet and try again"its an endless loop

Force restart the iPhone:

1. Press and quickly release the volume up button.
2. Press and quickly release the volume down button.
3. Press and hold the side button until you see the Apple logo (this might take longer than 10 seconds).
4. Press and quickly release the volume up button.
5. Press and quickly release the volume down button.
6. Press and hold the side button until you see the Apple logo (this might take longer than 10 seconds).

The operative word here is QUICKLY for the first two buttons, then a long hold for the SIDE button; and try it a couple of times, the timing is a little tricky. If done correctly this will always work unless the phone has a hardware problem. 

Restore your iOS device to factory settings - Apple Support