Trying to share iCloud Drive folder with Family Sharing, getting "Cannot Share Folder"

I have a 2TB iCloud+ (i.e. iCloud Drive) storage space plan with Apple.

I have set up Family Sharing on my MacBook Pro (Sequoia 15.0.1), and have successfully invited my wife to be included in Family Sharing on her MacBook Air (Sequoia 15.0.1). Both laptops show Family Sharing successfully set up, and both show my 2TB Drive as being shared.

My iCloud Drive has a top level folder called "Photos & Video" and inside that there is a large sub-structure of folders containing 25,000+ family photos and video clips. I've gone to that top level folder in Finder, done a "Get Info", and changed the permissions so that my wife can read and write, including all the items contained within that top level folder (i.e. the entire structure).

But when I go to icloud.com/iclouddrive and try to issue the invitation or link for her to share the Drive, it says "Cannot share Folder, try again later".

Any idea what I'm missing?