Hello,
Firstly, thank you for developing and maintaining DAVx⁵ and all other apps and libs from Bitfire!
I have to use Google Calendar for work and I use DAVx⁵ to access calendar events from my phone. It works very well except one detail: when I mark an event as “declined”, it is not marked as such on my phone. It’s a detail but I would prefer not to get reminders when I am not supposed to work 
To be more precise, my calendar app (Etar) shows my email address in the “NO” section but for the “attending” bit, nothing is checked: not Yes/Maybe/No:

I quickly looked at Etar’s source code and it seems they look at the “Attendee Status”: https://developer.android.com/reference/android/provider/CalendarContract.Attendees
From DavX⁵ logs, I can see that the iCal downloaded for the test event I created is properly retrieved:
PRODID:-//Google Inc//Google Calendar 70.9054//EN
VERSION:2.0
CALSCALE:GREGORIAN
X-WR-CALNAME:MY@EMAIL.ADDRESS
X-WR-TIMEZONE:Europe/Brussels
BEGIN:VTIMEZONE
TZID:Europe/Brussels
X-LIC-LOCATION:Europe/Brussels
BEGIN:DAYLIGHT
TZOFFSETFROM:+0100
TZOFFSETTO:+0200
TZNAME:CEST
DTSTART:19700329T020000
RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=-1SU
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:+0200
TZOFFSETTO:+0100
TZNAME:CET
DTSTART:19701025T030000
RRULE:FREQ=YEARLY;BYMONTH=10;BYDAY=-1SU
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
DTSTART;TZID=Europe/Brussels:20200721T164500
DTEND;TZID=Europe/Brussels:20200721T170000
DTSTAMP:20200721T144144Z
ORGANIZER;CN=MY@EMAIL.ADDRESS:mailto:MY@EMAIL.ADDRE
SS
UID:0nd7m6abt7p5mn55ijo5j8unat@google.com
ATTENDEE;CUTYPE=INDIVIDUAL;ROLE=REQ-PARTICIPANT;PARTSTAT=NEEDS-ACTION;CN=OT
HER@EMAIL.ADDRESS;X-NUM-GUESTS=0:mailto:OTHER@EMAIL.ADDRESS
ATTENDEE;CUTYPE=INDIVIDUAL;ROLE=REQ-PARTICIPANT;PARTSTAT=DECLINED;CN=MY@EMA
IL.ADDRESS;X-NUM-GUESTS=0:mailto:MY@EMAIL.ADDRESS
CREATED:20200721T144137Z
DESCRIPTION:
LAST-MODIFIED:20200721T144144Z
LOCATION:
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:test5
TRANSP:OPAQUE
BEGIN:VALARM
ACTION:DISPLAY
DESCRIPTION:This is an event reminder
TRIGGER:-P0DT0H2M0S
END:VALARM
END:VEVENT
END:VCALENDAR
(I replaced my email addresses and the invited one: I need at least two people to decline an event without cancelling it)
Later, we can see the event is added to the local calendar but with availability=0
: I guess it means ATTENDEE_STATUS_NONE, no?
2020-07-21 16:42:10 1073 [syncadapter.CalendarSyncManager] Adding 0nd7m6abt7p5mn55ijo5j8unat@google.com.ics to local calendar
PARAMETER #0 = Event=[alarms=[BEGIN:VALARM
ACTION:DISPLAY
DESCRIPTION:This is an event reminder
TRIGGER:-PT2M
END:VALARM
], attendees=[ATTENDEE;CUTYPE=INDIVIDUAL;ROLE=REQ-PARTICIPANT;PARTSTAT=NEEDS-ACTION;CN=OTHER@EMAIL.ADDRESS;X-NUM-GUESTS=0:mailto:OTHER@EMAIL.ADDRESS
, ATTENDEE;CUTYPE=INDIVIDUAL;ROLE=REQ-PARTICIPANT;PARTSTAT=DECLINED;CN=MY@EMAIL.ADDRESS;X-NUM-GUESTS=0:mailto:MY@EMAIL.ADDRESS
], categories=[], classification=null, color=null, description=, dtEnd=DTEND;TZID=Europe/Brussels:20200721T170000, dtStart=DTSTART;TZID=Europe/Brussels:20200721T164500, duration=null, exDates=[], exRules=[], exceptions=[], lastModified=LAST-MODIFIED:20200721T144144Z, location=, opaque=true, organizer=ORGANIZER;CN=MY@EMAIL.ADDRESS:mailto:MY@EMAIL.ADDRESS, rDates=[], rRules=[], recurrenceId=null, status=STATUS:CONFIRMED, summary=test5, unknownProperties=[CREATED:20200721T144137Z
], userAgents=[], sequence=0, uid=0nd7m6abt7p5mn55ijo5j8unat@google.com]
2020-07-21 16:42:10 1073 [AndroidEvent] Built event object
PARAMETER #0 = mType: 1, mUri: content://com.android.calendar/events?caller_is_syncadapter=true&account_name=Calendar%20Work&account_type=bitfire.at.davdroid&caller_is_syncadapter=true&account_name=Calendar%20Work&account_type=bitfire.at.davdroid, mSelection: null, mExpectedCount: null, mYieldAllowed: false, mValues: organizer=MY@EMAIL.ADDRESS description= allDay=0 accessLevel=3 hasAttendeeData=1 eventLocation= dtend=1595343600000 eventStatus=1 title=test5 eventEndTimezone=Europe/Brussels eventTimezone=Europe/Brussels calendar_id=5 dtstart=1595342700000 availability=0, mValuesBackReferences: null, mSelectionArgsBackReferences: null
2020-07-21 16:42:10 1073 [AndroidEvent] Built alarm 2 minutes before event
PARAMETER #0 = mType: 1, mUri: content://com.android.calendar/reminders?caller_is_syncadapter=true&account_name=Calendar%20Work&account_type=bitfire.at.davdroid, mSelection: null, mExpectedCount: null, mYieldAllowed: false, mValues: method=1 minutes=2, mValuesBackReferences: null, mSelectionArgsBackReferences: null
2020-07-21 16:42:10 1073 [AndroidEvent] Built attendee
PARAMETER #0 = mType: 1, mUri: content://com.android.calendar/attendees?caller_is_syncadapter=true&account_name=Calendar%20Work&account_type=bitfire.at.davdroid, mSelection: null, mExpectedCount: null, mYieldAllowed: false, mValues: attendeeEmail=OTHER@EMAIL.ADDRESS attendeeName=OTHER@EMAIL.ADDRESS attendeeType=1 attendeeRelationship=1 attendeeStatus=3, mValuesBackReferences: null, mSelectionArgsBackReferences: null
2020-07-21 16:42:10 1073 [AndroidEvent] Built attendee
PARAMETER #0 = mType: 1, mUri: content://com.android.calendar/attendees?caller_is_syncadapter=true&account_name=Calendar%20Work&account_type=bitfire.at.davdroid, mSelection: null, mExpectedCount: null, mYieldAllowed: false, mValues: attendeeEmail=MY@EMAIL.ADDRESS attendeeName=MY@EMAIL.ADDRESS attendeeType=1 attendeeRelationship=1 attendeeStatus=2, mValuesBackReferences: null, mSelectionArgsBackReferences: null
2020-07-21 16:42:10 1073 [AndroidEvent] Built unknown property: CREATED
(again I replaced email addresses)
Do you think it would be possible to set the attendee status to Accepted / Declined / Tentative by looking at the ATTENDEE
list from the iCal file and matching on the email address of the account? Or is it a configuration issue somewhere 
Have a good day!
Matt