Hey,
So Davinci does not allow power bins to take Compositions, Timelines, Fusion Comps etc.
Maybe one day it will allow, but for now, it is not possible.
I however can suggest something that I have done to counter this, are you familiar with Dynamic Project Switching?
I have a project that I have called "Playgrounds" and in here is where I store all my reusable content that can't go into power bins. I then use Dynamic Project Switching to be able to copy and paste across any bins, comps, etc and it will always copy over perfectly.
I am happy to explain how to do this if you do not know how.