The road to modern authentication for Exchange Online is littered with things to do. One action item is to check Apple iOS and iPad devices using Exchange ActiveSync to connect to mailboxes. If these devices were configured to connect to Exchange Online before iOS 12, they’re likely using basic authentication. Right now, the only way to move them to modern authentication is to remove Exchange from the mail app and add Exchange again. It’s a bump on the way to modern authentication in October 2022.