Mail app disappeared from my iPhone overnight

The Mail app disappeared from my iPhone last night while I was asleep. I did a chat online and was advised to restore the iPhone from a backup. In the meantime, I checked the Apple support site and learned that under the latest version of iOS, apps like Mail, though they can't be deleted, can be removed from the Home screen, but remain in the App Library. . I checked to see if that was what had happened, but Mail was NOT in the App Library. It and everything related to it had disappeared entirely from my iPhone. (It's a XR using the latest iOS). I've browsed this site, and it seems that other Apple-supplied apps are disappearing from other people's phones too. I've now restored the iPhone, and Mail is back; it's slowly downloading everything else. I'm guessing there must be some glitch with the latest iOS.