Indeed, we identified some visual issues when dark mode on iOS 13 is enabled and we're working on resolving them. I have logged a feedback item on your behalf regarding this feature:
Please follow the feedback item in order to get notified on status changes.
In the meantime, as you mentioned RadDataForm, you could change the editors background color through DataForm EditorStyle as described here: DataForm Editors Styling
In addition, you can go through the following useful SO topic about detecting whether dark mode is enabled in Xamarin.Form: https://stackoverflow.com/questions/57879523/how-to-check-for-dark-mode-in-xamarin-forms
Let me know if I can assist with anything else.
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