@yuri I am guessing based on the screenshot, because I only speak English and German
Looks like you want to fill the user profile on the Sign Up Screen:
You have to separate it into two steps, because you only can update the User collection when you are logged in:
SignUp with email and password -> Submit
You can use all simple fields of the User collection here, but no relations, dropdown.
Now the record is created in the User collection.
User is now logged in.
Update Logged in User Profile with all the details you want to collect.
As the user is now logged in you can use all the dropdown menus etc. to fill the data for the related collections.
@yuri There was an issue last week where we faced this bug. It has been resolved and you should be clear within your app now. You may need to re-link the screens.