TYPO3 Core

Hello, everyone. We are currently creating a TYPO3 10.4 website. The website only contains the basic sitepackage extension. The site itself should be available in several languages, which can also have sub-languages. All languages ​​should have a fallback. As a small example. We have 2 languages ​​+ the default language (can also be seen in the configuration attached).
The language en-de should refer to english (master) as a fallback. In TYPO3 itself I created the sys_languages ​​and also translated 1 page into all languages. I also created a test content item that was translated for english (master), but not for en-de. Strangely enough, instead of the english (master) translation, the content element of Default is displayed to me in the frontend. The page title, however, is from the en-de translation. Also applies to TYPO3 9, 10 and 11. Does anyone have a solution or is this a known bug?

languages:
- title: Default
  enabled: true
  languageId: 0
  base: /
  typo3Language: de
  locale: de_DE.UTF-8
  iso-639-1: de
  navigationTitle: Default
  hreflang: de
  direction: ltr
  flag: multiple

- title: english (master)
  enabled: true
  languageId: 1
  base: /en
  typo3Language: eu
  locale: en.UTF-8
  iso-639-1: en
  navigationTitle: english (master)
  hreflang: en
  direction: ltr
  flag: eu

- title: en-DE
  enabled: true
  languageId: 15
  base: /en-de
  typo3Language: de
  locale: en_DE.UTF-8
  iso-639-1: en
  navigationTitle: en-DE
  hreflang: en-de
  direction: ltr
  flag: de
  fallbackType: fallback
  fallbacks: "1"