Hi @Flo60, welcome to our forum!
I have translated your question to English as this is an International forum, please post any replies in English and it will be easier for me and other users to assist you.
To remove the developer options menu, you will need to reset the "Settings" application in the device. This will not affect any other settings you have made though.
To do that, go to Settings > Apps & notifications > See all xx apps > Settings > Storage > Clear data > OK.
I hope that helps! 
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