Hi @Fthtkn, welcome to our forum!
Your question has been translated 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.
Is this something that has started to occur recently and is that ads about the device or is it just advertisements for other services?
If they are not advertisements for the device, the demo mode is not activated and it's either coming from an open tab in Chrome, or if you have downloaded an application that contain ads and shows them outside the application.
You can easily test this by restarting your device in safe mode since downloaded applications aren't loaded in this mode.
Let me know if that helps!
