I found something strange in my test project, i wrote some characters in my editor ( Prosemirror + Yjs) and delete some by backspace, then checked the ydoc.
the ydoc.store.clients shows the operation of that delete operation as blow:
In CRDTs you can’t delete Items, because they represent meta-data that is needed for conflict resolution. But you can delete the content of an Item, to reduce the amount of content stored. This is what gc is about. It enables some functionality to remove content while ensuring that document can always sync.