Tacking on to the purchase comments: Around the same time, my child attempted to purchase "Minecraft Store Item 6" from the iOS App Store, but the purchase wasn't being reflected in Minecraft. So we requested and received an App Store refund for that purchase. The crashing issues seemed to occur shortly after that. I'm not sure what caused what though. (E.g. did the refund cause the crashing, or did the crashing cause the issue that prompted me to request a refund? Don't know.)
I (my child) have been experiencing this issue since late March. Can currently reproduce with "iPad7,11"; iOS 16.5.1; Minecraft 1.20.13. If the Microsoft account is not signed in, then the app does not crash. Crash is typically within 20 seconds of seeing the main Minecraft menu screen.
I'm having similar issues. On iPad the game crashes shortly after opening. It only seems to happen when my Microsoft account is signed-in to Minecraft (not as an anonymous user).
Minecraft v1.20.15 seems to have fixed the errors we were experiencing. The app does not close shortly after startup. I'm able to navigate the Marketplace. Good times. If you're still experiencing the error, maybe check which version you're running (found on the bottom right corner of the Minecraft main menu).
When I entered the Marketplace initially, I saw the "Incomplete Minecoin Purchase - Someone started a purchase with the billing account on this device. Would you like to complete the purchase with this account?" prompt, I selected "OK", and was able to access the Marketplace. I actually got the prompt twice - presumably once for each of the 2 failed-and-refunded App Store purchases I made back in March. It looks like I might've received MineCoins even though the purchase was refunded, but I could be mistaken. If so, at least it would be an error in my favor.