We are sorry to say that there is a bug in this version of Universalis (and Catholic Calendar), which started being distributed in the App Store yesterday.
If you are using the white-on-black text mode (“night mode”) then the app crashes when you try to open it.
You have two options:
Delete and reinstall the app. This will reset the display mode to its default setting, which is black-on-white, so the crash will not happen.
Wait for the next update, version 2.91. We submitted this to Apple four hours ago, with a request that they should review it rapidly. If they operate at their