Google Calendar replies not recognized

Steps to reproduce

1. Create an event and invite some external person who manages their calendar through Google Calendar.
2. Let the external person reply to your invitation directly via Google Calendar (without clicking in the Nextcloud invitation eMail that is sent to them).
3. See how you get an eMail from the persons Google account, telling you that they replied to your invitation.
4. See how in your Nextcloud calendar event, the participation status of the person is not updated.

Expected behavior

Nextcloud Calendar should notice these replies from external calendar servers and update the participation status.

In our experience, this is one of the main reasons for people to complain about Nextclouds incompatibilities regarding calendars.

Actual behavior

The replies from external calendar servers are not recognized and so the organizer of an event has no overview about external participation if someone did not click on the Nextcloud eMail link. And for the invited person it is not clear that they have to click the link, because they assume that they can reply using their calendar software they are always using.

Calendar app version

5.5.9

CalDAV-clients used

No response

Browser

No response

Client operating system

No response

Server operating system

No response

Web server

None

Database engine version

None

PHP engine version

None

Nextcloud version

31.0.12

Updated from an older installed version or fresh install

None

List of activated apps

Nextcloud configuration

Web server error log

Log file

Browser log

Additional info

No response

No files, tests, or entry points are identified in the issue. Start by locating the handling of incoming external calendar replies and participant status updates; done means a reply sent directly from Google Calendar updates the organizer's event status, with coverage for the described flow.