[Bug]: Declined event shows as busy in free/busy availability

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github OR Nextcloud Community Forum (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

When you decline an even/meet the time slot still shows as busy in free/busy availability.

Steps to reproduce

1. userA sends a meet to userB
2. userB decline the meet
3. userX checks userB free/busy slot and show as busy at tthat time that have the declined meet.

Expected behavior

Userb shows as free.

Installation method

Community Manual installation with Archive

Nextcloud Server version

28

Operating system

Debian/Ubuntu

PHP engine version

PHP 8.1

Web server

Apache (supported)

Database engine version

MariaDB

Is this bug present after an update or on a fresh install?

Fresh Nextcloud Server install

Are you using the Nextcloud Server Encryption module?

None

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

{
    "system": {
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
            "calendar.domain.tld"
        ],
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "dbtype": "mysql",
        "version": "27.1.11.3",
        "overwrite.cli.url": "https:\/\/calendar.domain.tld",
        "dbname": "***REMOVED SENSITIVE VALUE***",
        "dbhost": "***REMOVED SENSITIVE VALUE***",
        "dbport": "",
        "dbtableprefix": "oc_",
        "mysql.utf8mb4": true,
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "installed": true,
        "skeletondirectory": "",
        "defaultapp": "calendar",
        "session_lifetime": 14400,
        "remember_login_cookie_lifetime": 172800,
        "token_auth_enforced": true,
        "ldapProviderFactory": "OCA\\User_LDAP\\LDAPProviderFactory",
        "mail_from_address": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpmode": "smtp",
        "mail_sendmailmode": "smtp",
        "mail_domain": "***REMOVED SENSITIVE VALUE***",
        "mail_smtphost": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpport": "25",
        "maintenance": false,
        "theme": "",
        "loglevel": 2
    }
}

List of activated Apps

Enabled:
  - calendar: 4.7.12
  - circles: 27.0.1
  - cloud_federation_api: 1.10.0
  - contactsinteraction: 1.8.0
  - dav: 1.27.1
  - federatedfilesharing: 1.17.0
  - federation: 1.17.0
  - files: 1.22.0
  - files_reminders: 1.0.0
  - files_rightclick: 1.6.0
  - files_trashbin: 1.17.0
  - files_versions: 1.20.0
  - logreader: 2.12.0
  - lookup_server_connector: 1.15.0
  - nextcloud_announcements: 1.16.0
  - notifications: 2.15.0
  - oauth2: 1.15.2
  - password_policy: 1.17.0
  - privacy: 1.11.0
  - provisioning_api: 1.17.0
  - related_resources: 1.2.0
  - serverinfo: 1.17.0
  - settings: 1.9.0
  - systemtags: 1.17.0
  - theming: 2.2.0
  - twofactor_backupcodes: 1.16.0
  - updatenotification: 1.17.0
  - user_ldap: 1.17.0
  - user_status: 1.7.0
  - viewer: 2.1.0
  - workflowengine: 2.9.0
Disabled:
  - activity: 2.19.0 (installed 2.19.0)
  - admin_audit: 1.17.0
  - bruteforcesettings: 2.7.0
  - comments: 1.17.0 (installed 1.17.0)
  - dashboard: 7.7.0 (installed 7.7.0)
  - encryption: 2.15.0
  - files_external: 1.19.0
  - files_pdfviewer: 2.8.0 (installed 2.8.0)
  - files_sharing: 1.19.0 (installed 1.19.0)
  - firstrunwizard: 2.16.0 (installed 2.16.0)
  - photos: 2.3.0 (installed 2.3.0)
  - recommendations: 1.6.0 (installed 1.6.0)
  - sharebymail: 1.17.0 (installed 1.17.0)
  - support: 1.10.1 (installed 1.10.0)
  - survey_client: 1.15.0 (installed 1.15.0)
  - suspicious_login: 5.0.0
  - text: 3.8.1 (installed 3.8.0)
  - twofactor_totp: 9.0.0
  - weather_status: 1.7.0 (installed 1.7.0)

Nextcloud Signing status

No response

Nextcloud Logs

No response

Additional info

No response

Start by tracing the calendar free/busy availability handling for events that have been declined, then reproduce the listed userA, userB, and userX sequence. Done means a declined event no longer makes userB appear busy in the reported time slot.