Same issue after updating to 14. iPhone 8. "Mobile data update failed" and I tried all suggestions and nothing works. Apple in its infinite wisdom has decided to turn on auto updates in iOS 14 even if you had it turned off. Phone then proceeds to download new carrier settings which will promptly turn your iPhone into an iPod. Then of course you can't manually trigger an update of the bad mobile data update carrier settings because that option doesn't exist in iOS 14. And if that wasn't enough, they renamed all pertinent settings! "Carrier" is gone, so you can't follow the instructions of people who have solved the issue before. And now....silence from Cupertino. Way to go, Apple! Definitely worth paying almost $1k. Keep fixing what's not broken and breaking what works well, because "innovation".