Card modal becomes broken full-page state when opening attached file from Cloud, blocking further interaction

[LostinSpacetime]

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Describe the bug
When the "Use bigger card view" setting is enabled and a user clicks on an attached file (or a link to a Cloud file in the description), the expected behavior is that the file opens in the Nextcloud Viewer overlay. Instead, the card modal transitions into a broken state: it stops rendering as a centered dialog and instead expands to fill the entire page. The file viewer never appears.
In this broken state:

Close buttons (×, Esc) are unresponsive
The board behind the modal is no longer reachable
The only way out is the browser back button
After going back, clicking any card immediately re-opens the same broken modal state
Only a full page reload (F5/Ctrl+R) restores normal modal behavior

The card modal does still contain a working "open file" affordance in this state, so the file is theoretically reachable, but the UX is severely broken.
When "Use bigger card view" is disabled (sidebar mode), the same attachments open correctly in the Viewer.

To Reproduce
Steps to reproduce the behaviour:

1. Enable "Use bigger card view" in Deck settings
2. Open a card that has either:

• a Cloud file attached (via upload or "share from Files"), or
• a link to a Cloud file in the description

3. Click the attachment / link to open the file.
4. Modal expands to fill the page; viewer never opens; UI becomes partially unresponsive

Expected behaviour
File should be opened.

Client details:

• OS: Fedora 44
• Browser Chromium, Firefox

Server details

Operating system:
Ubuntu 22.04

Web server:
Apache

Database:
MariaDB

PHP version:
8.3

Nextcloud version: (see Nextcloud admin page)
33.0.3

Where did you install Nextcloud from:
Plesk App

Login as admin user into your Nextcloud and access
http://example.com/index.php/settings/integrity/failed
paste the results here.

List of activated apps:

:

• activity: 6.0.0
• admin_audit: 1.23.0
• announcementcenter: 7.3.0
• app_api: 33.0.0
• bruteforcesettings: 6.0.0
• calendar: 6.2.4
• cloud_federation_api: 1.17.0
• comments: 1.23.0
• contacts: 8.4.5
• contactsinteraction: 1.14.1
• dav: 1.36.0
• deck: 1.17.1
• drawio: 4.2.3
• drop_account: 3.0.0
• external: 8.0.1
• federatedfilesharing: 1.23.0
• files: 2.5.0
• files_downloadlimit: 5.1.0
• files_fulltextsearch: 33.0.0
• files_linkeditor: 1.1.24
• files_pdfviewer: 6.0.0
• files_reminders: 1.6.0
• files_sharing: 1.25.2
• files_trashbin: 1.23.0
• files_versions: 1.26.0
• firstrunwizard: 6.0.0
• forms: 5.2.7
• fulltextsearch: 33.0.0
• fulltextsearch_elasticsearch: 33.0.0
• groupfolders: 21.0.7
• guests: 4.7.0
• logreader: 6.0.0
• lookup_server_connector: 1.21.0
• nextcloud_announcements: 5.0.0
• notes: 5.0.0
• notifications: 6.0.0
• notify_push: 1.3.1
• oauth2: 1.21.0
• password_policy: 5.0.0
• photos: 6.0.0
• polls: 9.0.7
• privacy: 5.0.0
• profile: 1.2.0
• provisioning_api: 1.23.0
• qownnotesapi: 26.2.2
• quota_warning: 1.23.0
• recommendations: 6.0.0
• related_resources: 4.0.0
• richdocuments: 10.1.3
• serverinfo: 5.0.0
• settings: 1.16.0
• sharebymail: 1.23.0
• side_menu: 5.3.0
• support: 5.0.0
• survey_client: 5.0.0
• systemtags: 1.23.0
• tasks: 0.17.1
• text: 7.0.1
• theming: 2.8.0
• twofactor_backupcodes: 1.22.0
• twofactor_totp: 15.0.0
• updatenotification: 1.23.0
• user_status: 1.13.0
• viewer: 6.0.0
• weather_status: 1.13.0
• webhook_listeners: 1.5.0
• workflowengine: 2.15.0

Nextcloud configuration:
{
"system": {
"passwordsalt": "REMOVED SENSITIVE VALUE",
"secret": "REMOVED SENSITIVE VALUE",
"trusted_domains": [
"cloud.schloss-schule.wien",
"localhost",
"116.202.135.22"
],
"datadirectory": "REMOVED SENSITIVE VALUE",
"dbtype": "mysql",
"version": "33.0.3.2",
"overwrite.cli.url": "https://cloud.schloss-schule.wien",
"dbname": "REMOVED SENSITIVE VALUE",
"dbhost": "REMOVED SENSITIVE VALUE",
"dbport": "",
"dbtableprefix": "oc_",
"dbuser": "REMOVED SENSITIVE VALUE",
"dbpassword": "REMOVED SENSITIVE VALUE",
"installed": true,
"instanceid": "REMOVED SENSITIVE VALUE",
"mail_smtpmode": "smtp",
"mail_sendmailmode": "smtp",
"mail_from_address": "REMOVED SENSITIVE VALUE",
"mail_domain": "REMOVED SENSITIVE VALUE",
"mail_smtphost": "REMOVED SENSITIVE VALUE",
"mail_smtpauthtype": "LOGIN",
"simpleSignUpLink.shown": false,
"maintenance": false,
"maintenance_window_start": 1,
"mysql.utf8mb4": true,
"default_language": "de_DE",
"default_locale": "de_AT",
"default_phone_region": "AT",
"app_install_overwrite": [
"auto_mail_accounts",
"whiteboard",
"discoursesso",
"deck",
"side_menu",
"onlyoffice",
"richdocumentscode",
"richdocuments",
"forms",
"qownnotesapi",
"appointments"
],
"theme": "",
"loglevel": 3,
"memcache.local": "\OC\Memcache\APCu",
"memcache.locking": "\OC\Memcache\Redis",
"memcache.distributed": "\OC\Memcache\Redis",
"redis": {
"host": "REMOVED SENSITIVE VALUE",
"port": 6379
},
"updater.release.channel": "stable",
"ldapIgnoreNamingRules": false,
"overwritehost": "cloud.schloss-schule.wien",
"auth.bruteforce.protection.enabled": true,
"app.mail.verify-tls-peer": false,
"encryption.legacy_format_support": false,
"encryption.key_storage_migrated": false,
"mail_smtpauth": true,
"mail_smtpname": "REMOVED SENSITIVE VALUE",
"mail_smtppassword": "REMOVED SENSITIVE VALUE",
"allow_local_remote_servers": true,
"trusted_proxies": "REMOVED SENSITIVE VALUE",
"enable_previews": true,
"enabledPreviewProviders": [
"OC\Preview\Movie",
"OC\Preview\PNG",
"OC\Preview\JPEG",
"OC\Preview\GIF",
"OC\Preview\BMP",
"OC\Preview\XBitmap",
"OC\Preview\MP3",
"OC\Preview\MP4",
"OC\Preview\TXT",
"OC\Preview\MarkDown",
"OC\Preview\PDF"
],
"session_keepalive": true,
"forbidden_filename_basenames": [
"con",
"prn",
"aux",
"nul",
"com0",
"com1",
"com2",
"com3",
"com4",
"com5",
"com6",
"com7",
"com8",
"com9",
"com\u00b9",
"com\u00b2",
"com\u00b3",
"lpt0",
"lpt1",
"lpt2",
"lpt3",
"lpt4",
"lpt5",
"lpt6",
"lpt7",
"lpt8",
"lpt9",
"lpt\u00b9",
"lpt\u00b2",
"lpt\u00b3"
],
"forbidden_filename_characters": [
"<",
">",
":",
""",
"|",
"?",
"*",
"\",
"/"
],
"forbidden_filename_extensions": [
" ",
".",
".part"
],
"group_based_user_listing": true,
"defaultapp": "",
"mail_smtpport": "465"
}
}