Attachments containing german special characters (Umlaut) are not shown in Notes

Error: Notes does not show attachments that are uploaded from files containing german special characters in their file name.

Steps:

1. Create empty note
2. Upload "test.pdf" → shown correctly
3. Rename "test.pdf" to "Übertest.pdf" locally before upload
4. Upload "Übertest.pdf" → ERROR, not shown

#Screenshot

Notes app version: 4.12.2

• Nextcloud version: Nextcloud Hub 9 (30.0.13)
• OS: Ubuntu 22
• Web server: apache2
• PHP version: 8.3
• Database: Mysql 8.0

Nextcloud configuration:

{
"system": {
"instanceid": "REMOVED SENSITIVE VALUE",
"passwordsalt": "REMOVED SENSITIVE VALUE",
"secret": "REMOVED SENSITIVE VALUE",
"trusted_domains": [
"314159.wolkesicher.de"
],
"datadirectory": "REMOVED SENSITIVE VALUE",
"dbtype": "mysql",
"version": "30.0.13.1",
"overwrite.cli.url": "https://314159.wolkesicher.de",
"dbname": "REMOVED SENSITIVE VALUE",
"dbhost": "REMOVED SENSITIVE VALUE",
"dbport": "",
"dbtableprefix": "",
"mysql.utf8mb4": true,
"dbuser": "REMOVED SENSITIVE VALUE",
"dbpassword": "REMOVED SENSITIVE VALUE",
"installed": true,
"integrity.check.disabled": true,
"enable_previews": true,
"loglevel": "4",
"mail_smtpmode": "smtp",
"mail_smtpauthtype": "PLAIN",
"mail_domain": "REMOVED SENSITIVE VALUE",
"mail_from_address": "REMOVED SENSITIVE VALUE",
"mail_smtpname": "REMOVED SENSITIVE VALUE",
"mail_smtppassword": "REMOVED SENSITIVE VALUE",
"mail_smtphost": "REMOVED SENSITIVE VALUE",
"mail_smtpport": "587",
"mail_sendmailmode": "smtp",
"mail_smtpauth": true,
"simpleSignUpLink.shown": false,
"versions_retention_obligation": "10,30",
"trashbin_retention_obligation": "10,30",
"activity_expire_days": "30",
"quota_include_external_storage": false,
"upgrade.disable-web": false,
"appcodechecker": false,
"config_is_read_only": false,
"filesystem_check_changes": "0",
"check_data_directory_permissions": false,
"log_type": "syslog",
"syslog_tag": "Nextcloud-oc39977",
"check_for_working_htaccess": false,
"check_for_working_wellknown_setup": false,
"has_internet_connection": true,
"updatechecker": false,
"session_lifetime": 86400,
"remember_login_cookie_lifetime": 86400,
"knowledgebaseenabled": false,
"tempdirectory": "/home/oc39977/tmp",
"session_keepalive": false,
"auto_logout": false,
"files_external_allow_create_new_local": false,
"default_phone_region": "DE",
"maintenance_window_start": "1",
"onlyoffice": {
"verify_peer_off": true,
"editors_check_interval": "0"
},
"preview_max_memory": 1280,
"enabledPreviewProviders": [
"OC\Preview\BMP",
"OC\Preview\GIF",
"OC\Preview\JPEG",
"OC\Preview\Krita",
"OC\Preview\Markdown",
"OC\Preview\MP3",
"OC\Preview\OpenDocument",
"OC\Preview\PNG",
"OC\Preview\TXT",
"OC\Preview\XBitmap",
"OC\Preview\Imaginary",
"OC\Preview\Image",
"OC\Preview\HEIC",
"OC\Preview\TIFF",
"OC\Preview\Movie"
],
"redis": {
"host": "REMOVED SENSITIVE VALUE",
"port": 6379,
"timeout": 0,
"password": "REMOVED SENSITIVE VALUE"
},
"filelocking.enabled": true,
"memcache.locking": "\OC\Memcache\Redis",
"memcache.local": "\OC\Memcache\Redis",
"maintenance": false,
"bulkupload.enabled": false,
"appstoreenabled": true,
"appstoreurl": "https://apiato.com/v1",
"htaccess.RewriteBase": "/",
"default_language": "de",
"default_locale": "de_DE",
"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": [
" ",
".",
".filepart",
".part"
]
}
}

Client

Please complete the following information.

• FireFox 141.0
• OS: MacOS Sequoia 15.5

Reproduce the issue in the Notes app by uploading both test.pdf and Übertest.pdf, then trace the attachment upload and rendering flow to compare how the filenames are handled. Confirm the fix by verifying that attachments with German umlauts are uploaded and displayed correctly, while the existing ASCII filename case still works.