Cellular updated failed

Here is what Apple recommends for resolving that: If you see an Update Failed or Apple Pay Not Available alert after iOS update or restart - Apple Support

I’d assume that that Learn More would show this info, too.

So to confirm, you have followed the previously-linked Apple procedure for resolving failed updates (click here for details), and those procedures using a Mac or Windows system did not resolve this case?

If so, your iPhone may well have failed, and you will want to contact Apple Support and discuss your options. Use the Get Support link in the upper right corner of this web page to start a support call.