[Bug]: Calender shows 2h offset since 31.0.6

⚠️ 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

My Nextcloud got an update tonight to 31.0.6 and I did a occ app:update --all which restulted in:

All apps are up-to-date or no updates could be found

Yesterday everything in calendar app was in the correct timezone, but today everything starts 2h earlier. I've connected my calendar also to my iPhone Calendar App and my Outlook on Macbook - both are showing the correct times.

👍🏼 /etc/timezone on my Nextcloud server is "Europe/Berlin" which is correct.
👍🏼 /settings/user/availability is also set to "Europe - Belin" which is correct.

Steps to reproduce

1. Calendar entry with 31.0.5 starts and ends at my local timezone
2. Update to 31.0.6
3. Calendar entry with 31.0.6 starts and ends 2h earlier than my local timezone

Expected behavior

Calendar entry with 31.0.6 starts and ends at my local timezone

Nextcloud Server version

31

Operating system

Debian/Ubuntu

PHP engine version

PHP 8.3

Web server

Nginx

Database engine version

MariaDB

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

Updated from a MINOR version (ex. 32.0.1 to 32.0.2)

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": {
        "memcache.local": "\\OC\\Memcache\\APCu",
        "apps_paths": [
            {
                "path": "\/var\/www\/html\/apps",
                "url": "\/apps",
                "writable": false
            },
            {
                "path": "\/var\/www\/html\/custom_apps",
                "url": "\/custom_apps",
                "writable": true
            }
        ],
        "memcache.locking": "\\OC\\Memcache\\Redis",
        "redis": {
            "host": "***REMOVED SENSITIVE VALUE***",
            "port": 6379
        },
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
            "nextwurz.mooo.com",
            "nextcloud.rhoenwurz.de"
        ],
        "trusted_proxies": "***REMOVED SENSITIVE VALUE***",
        "forwarded_for_headers": [
            "HTTP_X_FORWARDED",
            "HTTP_FORWARDED_FOR"
        ],
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "dbtype": "mysql",
        "version": "31.0.6.2",
        "overwrite.cli.url": "https:\/\/nextwurz.mooo.com",
        "overwriteprotocol": "https",
        "dbname": "***REMOVED SENSITIVE VALUE***",
        "dbhost": "***REMOVED SENSITIVE VALUE***",
        "dbport": "3306",
        "dbtableprefix": "",
        "mysql.utf8mb4": true,
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "installed": true,
        "updater.release.channel": "stable",
        "mail_smtpmode": "smtp",
        "mail_smtpsecure": "ssl",
        "mail_sendmailmode": "smtp",
        "mail_smtpauth": 1,
        "mail_smtpauthtype": "LOGIN",
        "mail_smtphost": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpport": "465",
        "mail_from_address": "***REMOVED SENSITIVE VALUE***",
        "mail_domain": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpname": "***REMOVED SENSITIVE VALUE***",
        "mail_smtppassword": "***REMOVED SENSITIVE VALUE***",
        "twofactor_enforced": "false",
        "twofactor_enforced_groups": [],
        "twofactor_enforced_excluded_groups": [],
        "maintenance": false,
        "loglevel": 2,
        "app_install_overwrite": [
            "quota_warning",
            "occweb",
            "memories"
        ],
        "theme": "",
        "default_phone_region": "GER",
        "trashbin_retention_obligation": "auto,31",
        "maintenance_window_start": 1,
        "memories.exiftool": "\/var\/www\/html\/custom_apps\/memories\/bin-ext\/exiftool-amd64-musl",
        "memories.vod.path": "\/var\/www\/html\/custom_apps\/memories\/bin-ext\/go-vod-amd64",
        "enabledPreviewProviders": [
            "OC\\Preview\\Image"
        ],
        "preview_max_x": 2048,
        "preview_max_y": 2048,
        "memories.index.path.blacklist": ".hetzner|.pixx|\\\/Music|\\\/My .*|\\\/Videos",
        "memories.db.triggers.fcu": true
    }
}

List of activated Apps

Enabled:
  - activity: 4.0.0
  - admin_audit: 1.21.0
  - app_api: 5.0.2
  - bruteforcesettings: 4.0.0
  - calendar: 5.3.5
  - circles: 31.0.0
  - cloud_federation_api: 1.14.0
  - cloud_py_api: 0.2.0
  - contacts: 7.1.5
  - dav: 1.33.0
  - event_update_notification: 2.6.1
  - federatedfilesharing: 1.21.0
  - files: 2.3.1
  - files_downloadlimit: 4.0.0
  - files_external: 1.23.0
  - files_reminders: 1.4.0
  - files_retention: 2.0.1
  - files_sharing: 1.23.1
  - files_trashbin: 1.21.0
  - firstrunwizard: 4.0.0
  - forms: 5.1.2
  - logreader: 4.0.0
  - lookup_server_connector: 1.19.0
  - mediadc: 0.4.0
  - memories: 7.6.0
  - nextcloud_announcements: 3.0.0
  - notifications: 4.0.0
  - oauth2: 1.19.1
  - password_policy: 3.0.0
  - photos: 4.0.0-dev.1
  - previewgenerator: 5.8.0
  - privacy: 3.0.0
  - profile: 1.0.0
  - provisioning_api: 1.21.0
  - quota_warning: 1.21.0
  - recognize: 9.0.3
  - related_resources: 2.0.0
  - serverinfo: 3.0.0
  - settings: 1.14.0
  - sharebymail: 1.21.0
  - spreed: 21.1.1
  - survey_client: 3.0.0
  - theming: 2.6.1
  - twofactor_backupcodes: 1.20.0
  - updatenotification: 1.21.0
  - viewer: 4.0.0
  - webhook_listeners: 1.2.0
  - workflowengine: 2.13.0
Disabled:
  - comments: 1.21.0 (installed 1.5.0)
  - contactsinteraction: 1.12.0 (installed 1.1.0)
  - dashboard: 7.11.0 (installed 6.0.0)
  - encryption: 2.19.0
  - federation: 1.21.0 (installed 1.5.0)
  - files_pdfviewer: 4.0.0 (installed 4.0.0)
  - files_versions: 1.24.0 (installed 1.17.0)
  - maps: 1.5.0 (installed 1.5.0)
  - recommendations: 4.0.0 (installed 0.8.0)
  - support: 3.0.0 (installed 1.0.0)
  - suspicious_login: 9.0.1 (installed 7.0.0)
  - systemtags: 1.21.1 (installed 1.5.0)
  - text: 5.0.0 (installed 3.1.0)
  - twofactor_nextcloud_notification: 5.0.0
  - twofactor_totp: 13.0.0-dev.0
  - user_ldap: 1.22.0
  - user_status: 1.11.0 (installed 1.1.1)
  - weather_status: 1.11.0 (installed 1.0.0)

Nextcloud Signing status

No errors have been found.

Nextcloud Logs

Additional info

No response

No source file or test is named in the report. Start by reproducing the Europe/Berlin calendar-entry comparison on versions 31.0.5 and 31.0.6, then trace the calendar time display and timezone handling. Done means entries retain the correct local time after updating to 31.0.6, with a regression test covering the offset.