My son and I have had the same issue for approximately the past day. Both on iOS 13.3, me on an iPhone X and him on an iPad Air (3rd gen). Initially the app would freeze after a few minutes of play on either local LAN worlds or on realms, and then it got worse. Now we cannot get past the initial Mojang screen. The app freezes after getting about 75% of the way through the initial load.
I'm having this exact issue as is my son. I've found that I can connect occasionally when using cellular service, but the app freezes within minutes regardless of mode of play. I've uninstalled the app and recreated some local worlds and everything works fine until I attempt to log into Xbox Live at which point it immediately freezes and subsequent attempts to open the app freeze as well. I'm on an iPhone X with iOS 13.3 and my son is on an iPad Air with the same iOS.