Using Outlook for iOS for personal email and calendar management
Good Day! Thank you for the information, and I apologize for any inconvenience this situation has caused. I've been researching this issue, Outlook app (v4.2227.) crashes upon startup on a few iPad and iPhones running iOS15.5, is a known issue that the Microsoft product team investigated it and they are working on it. We are hoping that they will solve it as soon as possible.
Thank you for your time and understanding.
Sincerely,
De Paul | Microsoft Community Moderator