I really want this feature too!
The other day I asked ChatGPT for a solution for this - because I really need this so badly! But it only gives me some stupid answers 
For now, the only non-techy walkaround is duplicating the member-only article, and sharing preview via draft.
but the problem comes when you edit the original post. it doesn’t automatically update another draft version (for sharing with your friends) .
I still need to find a way to sync between the original post and this draft post content, thought.
Is there a smarter way making this secretlink happen by building a small middle-ware which grant the access via API or something? 