Users in Germany would set German age ratings (FSK xx) for movie and TV content (not any foreign rating system).
Any settings would automatically be overridden by the age for the Apple Account. A 14 y.o. would not be able to play FSK 16 rated content while on their own account, regardless of device settings.
Any custom (!) lower age restrictions would be set in System Settings﹥Screen Time﹥[ʀᴇsᴛʀɪᴄᴛɪᴏɴs] Content & Privacy﹥Store Restrictions﹥
﹥Movies﹥…
﹥TV Shows﹥…
If Content & Privacy is turned off, then no content restriction apply (except the account itself).
MDM might have additional restrictions, if the Mac is managed by a school or corporation.
If it doesn’t work for you as Apple describes in their support documents, then please consult with Apple Support. If they concur, then they may have a bug to fix for your country.
A few others have reported what I think are similar issues.