I don’t post on Facebook—HN is my closest analogue. But I assure you my partner(s) have no interest in seeing whatever I post here. Any more than I want to be in the thick of the extended-family group chats. Or, frankly, Facebook.
In that sense, maybe this is Facebook doing its part for domestic harmony…
I think the point was two people can be the absolute closest of friends, and Facebook will still fail to show them relevant posts.