@Thabor Thanks for the update! Probably there was some temporary problem.
Fastmail Carddav can't sync on Xiaomi (contact permissions)
Adding my fastmail account works. Caldav is syncing probably, carddav not. This happens when I generate an app password for mail, carddav, caldav and also when I generate one for the use of cardfav alone. Thanks for the help!
java.lang.SecurityException: Permission Denial: writing com.android.providers.contacts.ContactsProvider2 uri content://com.android.contacts/raw_contacts?account_name=Fastmail&account_type=bitfire.at.davdroid&caller_is_syncadapter=true from pid=13535, uid=10116 requires android.permission.WRITE_CONTACTS, or grantUriPermission()
DAVdroid doesn’t have the permission to write contacts. Please allow the permissions in DAVdroid, and see https://davdroid.bitfire.at/faq/entry/miui-no-synchronization/
Thanks! Now it works. Keep up the great work!