I wanted to use the PopUpButtonPickerStyle for my Picker which i use in a Form, but it just does not exist for me. Any other PickerStyle thats in the Apple documentation works.
Does anyone have an idea what could cause this?
It is clear from the Apple Documentation that PopUpButtonPickerStyle is only available on macOS 10.15+ and not on iOS.
Since you marked your question with the "ios" tag I am assuming you are building iOS app indeed and thus you cannot use it.