Cannot create calendar after update to Android 10

[asnelt]

I am running Offline-Calendar on a Pixel 3 with AOSP on Android 10 without Google apps. When I try to add a calendar, I get the message:

"Adding the calendar failed!
If you are using Cyanogenmod: Make sure that Privacy Guard is disabled for this application to allow calendar read/write. If you are using Android 4.3 App Ops: Make sure that you allow calendar read/write access for this application."

The app has the "Calendar" permission. No permissions denied.

I noticed the other issues on calendar adding, but for me it worked fine on Android 9 and only stopped working after upgrading to Android 10 so I assume that this is a different issue.