This is the message I got from ProtonMail support:
Jul 5, 2023, 09:13 GMT+2
Hello,
Thank you for your feedback.
Kindly note that our team is aware of the crash issue and we are working on fixing it as soon as possible, other users have experienced the same issue from their side.
In the meantime, as a last resort, you can go to the Google Play Store, search for the Proton Calendar app, and then go to ā Leave beta to see if the application will be stable again.
Update the app to the latest version (2.11.15)
Clear local data this is different from clearing cache open present in Proton Calendar app. To clear the local data, user must go to Android Settings ā Apps ā Manage Apps ā Search Proton Calendar ā Clear Data (may vary on different Android versions/flavors)
Log in again