with an expected class in shared, not possible to have any method implementation? All methods must be actualized in platform specific actuals? I have a class (decorator) that can have some of its methods actually implemented in shared - but am forced to duplicate the code in actuals. Is this (no pun intended) "expected"? Seems like a waste.

You could extract common parts to separate class. But it is more like workaround.

right, but not clean, and especially in this particular case - as I mentioned, it is a decorator around model data class (for some logical operations on the model), all methods really belong in this particular class