TYPO3 Core

Please take note that creating/uploading folders and files with
Umlauts works perfectly!

System should be configured the right way. What i checked:

System environment check it says:

- System locale is correct
- File names with UTF-8 characters can be used. ( [SYS][UTF8filesystem] = true )
- Your database uses utf-8. All good.

phpinfo and (this one in install tool) says:
intl.default_locale de-CH
default_charset utf-8

Checking on console all characters looks ok.

Configuring [SYS][systemLocale] = en_US.UTF-8 to something else installed in system does not make any difference.

Result is allways something similar to this (note the ???) in error message:

Core: Exception handler (WEB): Uncaught TYPO3 Exception: #1329647780: Object with identifier "1:/Jugend/?/???.txt" does not exist in storage | TYPO3\CMS\Core\Resource\Exception\ResourceDoesNotExistException thrown in file /var/www/webroot/ROOT/vendor/typo3/cms/typo3/sysext/core/Classes/Resource/ResourceFactory.php in line 565. Requested URL: https://devn.web.sac-cas.ch/typo3/index.php?route=%2Ffile%2Feditcontent&token=28ee451c0a0f5b64654d3c736c4643a2b236e64c&target=1%3A%2FJugend%2F%FC%2F%E4%F6%FC.txt&returnUrl=%2Ftypo3%2Findex.php%3FM%3Dfile_FilelistList%26moduleToken%3De2e018e00f1e91d34746687efed4571c998b56a7%26id%3D1%253A%252FJugend%252F%25C3%25BC%252F

Taking a simple script like this one: https://github.com/alexantr/filemanager
and using it on same server, has no problem with Umlauts or whatsoever.