The selected value is in the atttribute of the entity with the enumeration you have chosen. So if I have the entity Test with the attribute testenum that is connected to some enum. The enum slider you have placed on a form with the Test object on it.
In the on change microflow the object is passed, so based on the value in the testenum you can do the stuff you want, because the testenum attribute will hold the selected value.
Normally you don't need extra functionality to read or update the selected value, the widget should change the attribute of the object and that value is available in the microflow.
Edit: version from Github works here in 6.5.1