Animatable RNA properties in collections of collections


I am writing a modifier in which I have a collection property. My issue is that the sub-properties, of the elements of the collection, don’t seem to be animatable.

Before extracting a minimum (non-)working example I wanted to know whether it is actually possible to have these animatable, provided that they are in a collection (modifiers) of collection (within my modifier)? I could not find other examples of such a case in the codebase.