Unable to add events to federated calendar

Steps to reproduce

1. User A on Server A shares Calendar A to User B on Server B with edit permissions
2. User B tries to create an event but is unable to chose Calendar A

Expected behavior

It should be possible to select a federated calendar when creating events.

Actual behavior

The Nextcloud UI does not list the federated calendar in the calendar dropdown when creating an event.

Calendar app version

6.4.2

CalDAV-clients used

No response

Browser

Firefox 140.11.0esr (64-bit)

Client operating system

Debian GNU/Linux 13.5

Server operating system

Debian GNU/Linux 13.5

Web server

Apache

Database engine version

MariaDB

PHP engine version

PHP 8.4

Nextcloud version

33.0.5

Updated from an older installed version or fresh install

Updated from an older version

List of activated apps

Nextcloud configuration

Web server error log

Log file

Browser log

Additional info

It's still possible to create events with a client like Thunderbird so this does not seem to be a permissions or dav issue.

Reproduce the issue in the Nextcloud Calendar UI with a federated calendar shared with edit permissions, then trace the code that populates the calendar dropdown during event creation. Confirm that the federated calendar appears as a selectable option and that an event can be created, while preserving the existing Thunderbird behavior.