ICloud Folder Sharing Question

There is a new feature in IOS 13.4 for iCloud folder sharing. However it seems that it is only for folders you have created yourself,and not for any folder created by an app.

For example I am trying to share the Readle Documents folder but it is grayed out. Can’t figure any way around this.

Why is iCloud storage so complicated?

I believe it revolves around Apple’s conservative approaches to
security, although I can’t point to any tangible evidence that supports that.