Allow me to change the text "Do you already have an account?" below the social logins

this is the same on all screens, I can't change the text of the bottom most element

Yes. This is an automatically translated section. Sorry we can't accommodate this right now. But we are working on a major update to the auth experience which will give you full control of screens and all translations. See this roadmap item. https://updates.kinde.com/board/custom-sign-in-up-page

Just to follow up here @dachsteinhustler, forgive me here as I don't speak german. What is the difference between the the two messages between Sie and Du?

One is more formal than the other.

More traditional companies typically use "Sie", while more modern companies often use "Du".

I guess it's not a deal breaker, but if all of the actual app is already written in "Du", I thought it makes sense to have the login experience in "Du" as well.

Thank you for clarifying. You will be pleased to know that we have work happening now which will allow you to customise this. So while its not changeable now and you could change with the custom sign in pages as Claire pointed out, if you can live with it for little while longer what you're asking will be possible natively.

Oh further on this. You can raise issues against the Kinde translation files for consideration. For German, see https://github.com/kinde-oss/kinde-translations/tree/main/de

Your translations are totally fine, it's just that there are different ways to communicate.