how can i achive a floating action button in front of all other apps?
A java example could be: https://www.journaldev.com/14673/android-floating-widget.
What flutter widget can i use for that. Maybe there are some examples with flutter (didn't found any).
Thanks
You can perform the similar action using Draggable widget but that will work only inside the app and inside same Stateful/Stateless widget.
The reason why "drawing over other apps" is not possible in Flutter till yet is because iOS does not support this functionality. You can always log an issue at Flutter's GitHub repository