Cellular Data update failure

See this Apple support link-->If you see a Cellular Update Failed or Apple Pay Not Available alert after iOS update or restart - Apple Support

You need to call your carrier. Also have low power mode on at 90% doesn’t do your iPhone any favours. As it does refresh apps and restricts other things.

You MUST have iTunes version 12.9.4. Check the version. If it isn't 12.9.4 and you can't install that version you will have to take the phone to an Apple store or Apple Authorized Service Provider.

Just take in to an Apple Store. And get them to examine it.

There's no way of knowing, but if the link I posted first doesn't fix it most likely it's hardware.