I work a lot with (sometimes repeatedly nested) symbols, and even though you can add prototype functions with the default “None” as the target, as far as I know, you can’t define an animation type in this case.
Example app design:
I am missing a way to set a right-directed animation on the back icon and a slide-up function with different speeds for the action icon in a simple navigation bar where icons and actions can be optionally displayed. However, it would not be enough to set the default animation for this interaction, where the target is not known, because instead of a back button and a slide right animation, I might also need a close of a modal, which should allow an overwrite from slide right to slide down. I hope you get the idea…
In connection with this, there was probably already the question in this feature request Select layers inside a symbol when prototyping - #8 by jkilp as to whether the links wouldn’t make more sense in the prototype tab instead of the design tab and that drag+drop would be a great addition. #push