I wonder if there is some kind of widget that fades out as soon as some time passes.
Something like that:
child: Temporary(500, child: Text("I will disappear in 500ms"))
If it does not exist in a package or build-in yet - what would be a good way to solve this by myself?
You could make use of the AnimatedOpacity widget.
There is a cookbook with detailed description. But instead of using a button to toggle the visibility, you could make use of a Timer() call which fires once, has a Duration set to 500 ms and a callback that changes the visibility boolean.
The link:
https://docs.flutter.dev/cookbook/animation/opacity-animation