2 hours gab between Deck and Calendar

To Reproduce
Steps to reproduce the behavior:

1. Go to Deck
2. Create a new card with due time set to 12:00
3. Go To Calendar
4. Search and Click on the same task
5. See error : task due for 10:00 !!
   PS : my timestamp is set to Europe/Paris so we have 2 hours more than the sun time
   PS'' : sorry for my english

Expected behavior
A new card should appear in the Calendar App with the same hours

Screenshots
If applicable, add screenshots to help explain your problem : see PJ

Client details:
armbian
firefox 88.0.1
PC Ubuntu 20.04

PHP version:
7.3

Nextcloud version:
21.0:2:1
Where did you install Nextcloud from:
NextcloudPi

Login as admin user into your Nextcloud and access
No errors have been found.

**List of activated apps:**
Enabled:
  - accessibility: 1.7.0
  - activity: 2.14.3
  - bruteforcesettings: 2.1.0
  - calendar: 2.2.2
  - cloud_federation_api: 1.4.0
  - comments: 1.11.0
  - contacts: 3.5.1
  - contactsinteraction: 1.2.0
  - dashboard: 7.1.0
  - dav: 1.17.1
  - deck: 1.4.2
  - federatedfilesharing: 1.11.0
  - federation: 1.11.0
  - files: 1.16.0
  - files_pdfviewer: 2.1.0
  - files_rightclick: 1.0.0
  - files_sharing: 1.13.1
  - files_trashbin: 1.11.0
  - files_versions: 1.14.0
  - files_videoplayer: 1.10.0
  - firstrunwizard: 2.10.0
  - groupfolders: 9.0.1
  - logreader: 2.6.0
  - lookup_server_connector: 1.9.0
  - news: 15.4.5
  - nextcloud_announcements: 1.10.0
  - notes: 4.0.4
  - notifications: 2.9.0
  - oauth2: 1.9.0
  - password_policy: 1.11.0
  - photos: 1.3.0
  - privacy: 1.5.0
  - provisioning_api: 1.11.0
  - recommendations: 1.0.0
  - serverinfo: 1.11.0
  - settings: 1.3.0
  - sharebymail: 1.11.0
  - support: 1.4.0
  - survey_client: 1.9.0
  - systemtags: 1.11.0
  - tasks: 0.13.6
  - text: 3.2.0
  - theming: 1.12.0
  - twofactor_backupcodes: 1.10.0
  - updatenotification: 1.11.0
  - user_status: 1.1.1
  - viewer: 1.5.0
  - weather_status: 1.1.0
  - workflowengine: 2.3.0
Disabled:
  - admin_audit
  - encryption
  - files_external
  - nextcloudpi
  - previewgenerator
  - user_ldap


**Nextcloud configuration:**

{
    "system": {
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": {
            "0": "localhost",
            "1": "192.168.1.15",
            "5": "nextcloudpi.local",
            "7": "nextcloudpi",
            "8": "nextcloudpi.lan",
            "12": "flts.hopto.org",
            "21": "193.248.196.216",
            "20": "flts.hopto.org",
            "22": "192.168.1.3",
            "11": "90.13.255.105",
            "3": "flts.hopto.org",
            "2": "flts.hopto.org"
        },
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "dbtype": "mysql",
        "version": "21.0.2.1",
        "overwrite.cli.url": "https:\/\/192.168.1.15\/",
        "dbname": "***REMOVED SENSITIVE VALUE***",
        "dbhost": "***REMOVED SENSITIVE VALUE***",
        "dbport": "",
        "dbtableprefix": "oc_",
        "mysql.utf8mb4": true,
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "installed": true,
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "memcache.local": "\\OC\\Memcache\\APCu",
        "memcache.distributed": "\\OC\\Memcache\\Redis",
        "memcache.locking": "\\OC\\Memcache\\Redis",
        "redis": {
            "host": "***REMOVED SENSITIVE VALUE***",
            "port": 0,
            "timeout": 1.5,
            "password": "***REMOVED SENSITIVE VALUE***"
        },
        "tempdirectory": "\/media\/serverFLTS\/nextcloud\/ncdata\/tmp",
        "mail_smtpmode": "sendmail",
        "mail_smtpauthtype": "LOGIN",
        "mail_from_address": "***REMOVED SENSITIVE VALUE***",
        "mail_domain": "***REMOVED SENSITIVE VALUE***",
        "preview_max_x": "2048",
        "preview_max_y": "2048",
        "jpeg_quality": "60",
        "overwriteprotocol": "https",
        "maintenance": false,
        "logfile": "\/media\/serverFLTS\/ncdata\/nextcloud.log",
        "loglevel": "2",
        "log_type": "file",
        "theme": "",
        "mail_sendmailmode": "pipe"
    }
}

**Are you using an external user-backend, if yes which one:** LDAP/ActiveDirectory/Webdav/...
no


![bugDeck](https://user-images.githubusercontent.com/6138109/119909832-1ed06a80-bf56-11eb-802e-ba019d2d5da7.png)

Reproduce the issue by creating a Deck card due at 12:00 in the Europe/Paris timezone, then opening the same task in Calendar. Inspect the Deck-to-Calendar time handling; done means the Calendar entry shows the same due time as the card.