Yes! This is the answer!!!

Glad you got it! Just to clarify… by directly selected I meant a user selecting it in the family activity picker. If that isn’t working, then (at least as of iOS 16.4) it is probably something in your code.

Further update: I submitted an Apple Developer Code level Technical Support incident about this issue (pretty much put exactly what I posted here on the forum). After waiting a few days for a response this was their reply: "Thank you for contacting Apple Developer Technical Support (DTS). We have reviewed your request and have concluded that there is no supported way to achieve the desired functionality given the currently shipping system configurations."

:-(