[Bug]: Themed icon not used for shared links

⚠️ This issue respects the following points: ⚠️

[X] This is a bug, not a question or a configuration/webserver/proxy issue.
[X] This issue is not already reported on Github (I've searched it).
[X] Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
[X] Nextcloud Server is running on 64bit capable CPU, PHP and OS.
[X] I agree to follow Nextcloud's Code of Conduct.

Bug description

Even though all icons were changes by svg in Theming app, still when sharing a link, e.g. on iMessage (Apple iPhone), it shows a Nexcloud logo

Strangely enough (not sure if related), the HTML page also references still a core/img/favicon-mask.svg (which is the Nextcloud logo, and not modified on theming).

Steps to reproduce

Set as admin your own logos, background image, top menu logo and favicon (all uploaded as svg)
Go to your iPhone, get yourself a sharing link from a file in NExtcloud
Paste it in a new iMessage

Expected behavior

Show the correctly rendered uploaded custom icon on a colour as selected as background

Installation method

Community Manual installation with Archive

Operating system

Debian/Ubuntu

PHP engine version

PHP 8.0

Web server

Apache (supported)

Database engine version

MySQL

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

Fresh Nextcloud Server install

Are you using the Nextcloud Server Encryption module?

Encryption is Disabled

What user-backends are you using?

[X] 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": [
            "cloud.habelschwerdt.de"
        ],
        "theme": "habelschwerdt",
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "dbtype": "mysql",
        "version": "26.0.0.11",
        "overwrite.cli.url": "https:\/\/cloud.habelschwerdt.de",
        "dbname": "***REMOVED SENSITIVE VALUE***",
        "dbhost": "***REMOVED SENSITIVE VALUE***",
        "dbport": "",
        "dbtableprefix": "oc_",
        "mysql.utf8mb4": true,
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "installed": true,
        "overwritehost": "cloud.habelschwerdt.de",
        "overwriteprotocol": "https",
        "app_install_overwrite": [
            "extract",
            "mindmap_app",
            "files_linkeditor",
            "files_mindmap"
        ],
        "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",
        "mail_smtpauth": 1,
        "mail_smtpname": "***REMOVED SENSITIVE VALUE***",
        "mail_smtppassword": "***REMOVED SENSITIVE VALUE***",
        "memcache.local": "\\OC\\Memcache\\APCu",
        "memcache.distributed": "\\OC\\Memcache\\Memcached",
        "memcached_servers": [
            [
                "127.0.0.1",
                11211
            ]
        ],
        "default_phone_region": "DE",
        "maintenance": false
    }
}

List of activated Apps

Enabled:
  - activity: 2.18.0
  - admin_audit: 1.16.0
  - calendar: 4.3.1
  - circles: 26.0.0
  - cloud_federation_api: 1.9.0
  - collectives: 2.3.0
  - comments: 1.16.0
  - contacts: 5.2.0
  - contactsinteraction: 1.7.0
  - dashboard: 7.6.0
  - dav: 1.25.0
  - deck: 1.9.0
  - external: 5.1.0
  - federatedfilesharing: 1.16.0
  - federation: 1.16.0
  - files: 1.21.1
  - files_linkeditor: 1.1.13
  - files_pdfviewer: 2.7.0
  - files_rightclick: 1.5.0
  - files_sharing: 1.18.0
  - files_trashbin: 1.16.0
  - files_versions: 1.19.1
  - firstrunwizard: 2.15.0
  - logreader: 2.11.0
  - lookup_server_connector: 1.14.0
  - news: 21.1.0
  - nextcloud_announcements: 1.15.0
  - notifications: 2.14.0
  - oauth2: 1.14.0
  - password_policy: 1.16.0
  - polls: 4.1.8
  - privacy: 1.10.0
  - provisioning_api: 1.16.0
  - recommendations: 1.5.0
  - related_resources: 1.1.0-alpha1
  - richdocuments: 8.0.0
  - serverinfo: 1.16.0
  - settings: 1.8.0
  - sharebymail: 1.16.0
  - sociallogin: 5.4.2
  - spreed: 16.0.1
  - support: 1.9.0
  - survey_client: 1.14.0
  - systemtags: 1.16.0
  - text: 3.7.2
  - theming: 2.1.1
  - twofactor_backupcodes: 1.15.0
  - twofactor_totp: 8.0.0-alpha.0
  - updatenotification: 1.16.0
  - user_status: 1.6.0
  - viewer: 1.10.0
  - weather_status: 1.6.0
  - workflowengine: 2.8.0
Disabled:
  - bruteforcesettings: 2.6.0
  - encryption: 2.14.0
  - files_external: 1.18.0
  - mail: 3.0.2 (installed 3.0.2)
  - notes: 4.7.2 (installed 4.7.2)
  - photos: 2.2.0 (installed 2.2.0)
  - suspicious_login: 4.4.0
  - user_ldap: 1.16.0

Nextcloud Signing status

No errors have been found.

Nextcloud Logs

N/A

Additional info

No response

nextcloud / server